Hugo F V Cardoso
email: hfcardoso@fc.ul.pt

Yann Heuzé

Paula Júlio

Secular Change in the Timing of Dental Root Maturation in Portuguese Boys and Girls

Although secular changes in human growth are frequently reported in the literature, a secular trend in dental maturation has not been consistently shown to date. Objectives: In this study, we compare root formation in a modern sample of living Portuguese children (n = 521), between 6 and 18 years of age, with that of a similar sample of known sex and age Portuguese child skeletons (n = 114), who lived half a century earlier, to assess secular change in dental maturation. Methods: The roots of seven developing permanent mandibular teeth were assessed for their maturation in both samples. The median age-of-attainment of root stages was calculated using logistic regression and compared between the samples. The potential influence of mortality bias in root development of the skeletal sample was tested. Results: No mortality bias effect was detected. We find that the dentition of modern Portuguese boys and girls mature on average 1.22 years and 1.47 years earlier, respectively, compared to their counterparts born one half a century before. Our results also suggest that an earlier timing of attainment of root formation maturational stages was not accompanied by a change in the overall duration of root formation. Conclusions: We demonstrate a clear and consistent acceleration in dental root maturation due to secular changes and show that the plasticity in dental development in response to environmental factors is greater than previously thought.

The purpose of this study is to compare timing and duration of tooth formation in a sample of modern children from Portugal with that of a similar sample of children who were born and lived half a century earlier, and assess a secular trend in dental maturation. Secular trend or change refers to the process of "children getting larger and growing to maturity more rapidly" (Eveleth and Tanner, 1990: 205). These changes are related to the material conditions of life which act upon human growth over generations. A common explanation for these secular changes is the improved quantity and quality of nutrition, the reduction of infectious disease burden brought by immunization and sanitation and increased access to health and medical care [START_REF] Bogin | Patterns of human growth[END_REF][START_REF] Eveleth | Worldwide variation in human growth[END_REF][START_REF] Malina | Research on secular trends in auxology[END_REF][START_REF] Susanne | Living conditions and secular trend[END_REF][START_REF] Tanner | Fetus into Man: Physical Growth from Conception to Maturity[END_REF]. Secular changes in body size [START_REF] Cole | Secular trends in growth[END_REF][START_REF] Olds | One hundred years of growth: the evolution of height, mass, and body composition in Australian children, 1899-1999[END_REF][START_REF] Susanne | Changements séculaires de la croissance et du développement en Europe[END_REF], body composition (Freedman et al., 1991;[START_REF] Olds | One hundred years of growth: the evolution of height, mass, and body composition in Australian children, 1899-1999[END_REF][START_REF] Thompson | Secular trend in the development of fatness during childhood and adolescence[END_REF], tempo of growth [START_REF] Hermanussen | Plasticity of adolescent growth in boys[END_REF]Kalberg, 2002) and timing of sexual maturation [START_REF] Jones | Age at menarche and the evidence for a positive secular trend in urban South Africa[END_REF]Padez, 2002;[START_REF] Susanne | Changements séculaires de la croissance et du développement en Europe[END_REF] have occurred during the last century and are well documented for most industrialized countries and several developing nations. It is an improvement in socioeconomic conditions, such as the European and North American economic recovery sparked by World War II, which causes the material conditions of life to change and, consequently, human growth [START_REF] Bogin | Patterns of human growth[END_REF][START_REF] Eveleth | Worldwide variation in human growth[END_REF][START_REF] Malina | Research on secular trends in auxology[END_REF][START_REF] Susanne | Living conditions and secular trend[END_REF][START_REF] Tanner | Fetus into Man: Physical Growth from Conception to Maturity[END_REF]. Similarly, a decline in overall living conditions can also result in a persistent decrease in body size or delayed maturation, in which case the trend is inverted and a negative secular change occurs [START_REF] Bogin | Patterns of human growth[END_REF][START_REF] Tobias | The negative secular trend[END_REF].

Despite the current evidence, secular changes in skeletal and dental development have rarely been investigated and are less well known. Secular acceleration in skeletal maturation has only been clearly demonstrated for British [START_REF] Himes | An early hand-wrist atlas and its implications for secular change in bone age[END_REF] and South African children [START_REF] Hawley | Secular trends in skeletal maturity in South Africa: 1962-2001[END_REF], from hand-wrist radiographs. Other studies have shown that earlier reference standards for epiphyseal union are not appropriate for ageing modern human skeletons in a forensic context, suggesting a secular acceleration in skeletal maturation (Langley-Shirley and Jantz, 2010; [START_REF] Meijerman | Variables affecting the probability of complete fusion of the medial clavicular epiphysis[END_REF]. [START_REF] Lin | New growth references for assessment of stature and skeletal maturation in Australians[END_REF], [START_REF] Ranjitkar | Stature and skeletal maturation of two cohorts of Australian children and young adults over the past two decades[END_REF], and [START_REF] Ahmed | TW2 and TW3 bone ages: time to change?[END_REF] have also examined changes over time in skeletal maturation, but a clear secular trend has not been detected in these studies.

Findings have been mixed with respect to secular changes in tooth eruption and emergence [START_REF] Clements | Time of eruption of permanent teeth in British children in 1947-8[END_REF][START_REF] Eskeli | Standards for permanent tooth emergence in Finnish children[END_REF][START_REF] Helm | Secular trend in tooth eruption: a comparative study of Danish school children of 1913 and 1965[END_REF][START_REF] Höuffding | Emergence of permanent teeth and onset of dental stages in Japanese children[END_REF][START_REF] Kerr | The effect of the premature loss of deciduous canines and molars on the eruption of their successors[END_REF][START_REF] Leroy | Impact of caries experience in the deciduous molars on the emergence of the successors[END_REF][START_REF] Liversidge | Variation in crown and root formation and eruption of human deciduous teeth[END_REF][START_REF] Niswander | Dental eruption, stature, and weight of Hiroshima children[END_REF][START_REF] Parner | A longitudinal study of time trends in the eruption of permanent teeth in Danish children[END_REF][START_REF] Rönnerman | The effect of early loss of primary molars on tooth eruption and space conditions. A longitudinal study[END_REF][START_REF] Rousset | Emergence of permanent teeth: secular trends and variance in a modern sample[END_REF][START_REF] Virtanen | Timing of eruption of permanent teeth: standard Finnish patient documents[END_REF][START_REF] Wedl | Eruption times of permanent teeth in children and young adolescents in Athens (Greece)[END_REF] but the detection of a secular acceleration in the timing or in duration of tooth formation [START_REF] Holtgrave | Acceleration in dental development: fact or fiction[END_REF][START_REF] Monge | Dental calcification stages of the permanent M1 and M2 in U.S. children of African American and European American ancestry born in the 1990s[END_REF][START_REF] Nadler | Earlier dental maturation: fact or fiction?[END_REF][START_REF] Price | A radiographic study of the impact of race and sex on 1st and 2nd molar development[END_REF][START_REF] Simpson | A radiographic study of the development of the human mandibular dentition[END_REF] has been even more difficult to demonstrate. No study has been able to consistently and unequivocally show secular changes in dental maturation and those which attempt it reveal some limitations.

First and foremost, the analysis of secular trend in dental maturation has been hampered by the lack of comparative historic samples. According to [START_REF] Liversidge | Dental age revisited[END_REF], a secular trend would need a comparative reference sample that antedates World War II, and all large dental radiographic studies are later than this. Although secular changes were prominent in the 20th century, they became particularly pronounced after World War II, with the improvement in living standards and increased urbanization which were favorable to growth [START_REF] Bogin | Patterns of human growth[END_REF]. The time periods previously considered are usually insignificant for major societal changes to take place. In addition, those studies that reported a secular acceleration of tooth formation have been hampered by the use of inappropriate statistical techniques. In these studies, age-of-attainment of individual tooth stages has been calculated as the mean age at a stage, by averaging the age of children who are at a certain stage [START_REF] Nadler | Earlier dental maturation: fact or fiction?[END_REF][START_REF] Price | A radiographic study of the impact of race and sex on 1st and 2nd molar development[END_REF]. This method is heavily influenced by sample size and age distribution, and it is particularly unsuitable for the most mature stage of formation [START_REF] Liversidge | Dental age revisited[END_REF][START_REF] Smith | Standards of human tooth formation and dental age assessment[END_REF]. Only a few studies [START_REF] Holtgrave | Acceleration in dental development: fact or fiction[END_REF][START_REF] Monge | Dental calcification stages of the permanent M1 and M2 in U.S. children of African American and European American ancestry born in the 1990s[END_REF][START_REF] Simpson | A radiographic study of the development of the human mandibular dentition[END_REF] have used cumulative distribution methods to infer a secular acceleration in dental development. Unfortunately, two of these [START_REF] Holtgrave | Acceleration in dental development: fact or fiction[END_REF][START_REF] Monge | Dental calcification stages of the permanent M1 and M2 in U.S. children of African American and European American ancestry born in the 1990s[END_REF] inferred a secular acceleration from comparisons with earlier published standards-the [START_REF] Moorrees | Age variation of formation stages for ten permanent teeth[END_REF] and [START_REF] Nolla | The development of the permanent teeth[END_REF] studies -and not from comparisons with earlier similar dental data.

Therefore, two important aspects need to be considered when analyzing possible secular changes in dental formation: (1) samples must be separated by a significant amount of time while maintaining comparability, and (2) appropriate statistical technique for estimating the mean age of attainment must be employed. In addition, it is critical to consider the age at a given dental stage (i.e. timing), and the time taken to complete enamel and dentine formation (i.e. duration) when interpreting possible secular changes. Here we compare dental maturation in a modern sample of living Portuguese children with that of a sample of known sex and age Portuguese child skeletons, who lived half a century earlier. These two samples provide a unique opportunity to assess secular changes because they reflect a fundamental improvement in the socioeconomic and living conditions of the Portuguese. The maturation of seven developing permanent mandibular teeth (excluding M3) was assessed in both samples. Because of the age range in the modern sample we were not able to study the whole maturation process and, consequently, we have only focused on the timing of root formation. The median age-of-attainment of root stages was calculated using logistic regression and secular acceleration in timing of root formation was assessed by comparing median age-ofattainment between the historic and modern samples. Secular changes in the duration of root formation were also examined by comparing differences in median age-of-attainment between consecutive stages in both samples. However, before we can compare dental development in a sample of living children with that in a sample of child skeletons, we need to address the issue of mortality bias [START_REF] Saunders | Growth Deficit in Survivors and Non-Survivors: Biological Mortality Bias in Subadult Skeletal Samples[END_REF][START_REF] Wood | The osteological paradox: Problems of inferring prehistoric health from skeletal samples[END_REF]. Mortality bias means that child skeletons may reflect delayed growth due to their compromised health status, which eventually led to their premature death and may not be representative of their living counterparts. Therefore, before comparing dental maturation between the two samples of children, we evaluate the potential effects of mortality bias in the skeletal sample, by comparing dental maturation of children who died of natural causes with that of children who died of accidental causes.

MATERIALS AND METHODS

Samples

We utilized two samples of Portuguese children, which are over 50 years apart from each other. The earlier sample, described as the historic sample, is comprised of known sex and age skeletons from two museum skeletal collections; the Lisbon and Coimbra collections. This sample is comprised of 114 (60 girls and 54 boys) individuals born between 1887and 1960in Central and Southern Portugal, who died in Coimbra and Lisbon between 1903and 1972. The majority of births (80%) occurred between 1910 and 1940, while most individuals (81%) died between 1920 and 1950. The individuals range in age between 6 and 18 years. Calendar ages were obtained by subtracting the date of birth from the date of death. These children are considered representative of the middle-to-low socioeconomic strata of the Lisbon and Coimbra population during the first half of the twentieth century, as inferred from their father's occupation stated in the birth record. These occupations include a large proportion of menial jobs. The Lisbon and Coimbra samples provide an extraordinary opportunity to assess the timing of tooth formation in earlier periods due to the fact that chronological age is known in these collections with great accuracy, from civil registration records. The skeletons in these collections have been obtained from abandoned burial plots at the local cemeteries in Lisbon and Coimbra, where temporary graves are cleared periodically for new internments. Once skeletonization is reached, the remains are exhumed and kept in small burial niches (ossuaries) for a rental fee. The remains are considered abandoned and, subsequently destroyed or reburied in the communal grave after several years of unpaid fees by the relatives. Prior to destruction or reburial, the remains are collected and curated by each Museum, under a special permit. For more details on the composition and history of these collections, see [START_REF] Rocha | Les collections ostéologiques humaines identifiées du Musée Anthropologique de l'Université de Coimbra[END_REF] and [START_REF] Cardoso | The collection of identified human skeletons housed at the Bocage Museum (National Museum of Natural History) in Lisbon, Portugal[END_REF].

The more recent sample, described as the modern sample, consists of patients attending the residency dental clinic at the Faculty of Dentistry of the University of Porto. This sample comprises 521 children (260 girls and 261 boys) born between 1985 and 1997, who were examined between 1998 and 2006. The age range is identical to the historic sample (6-18 years) and calendar ages were calculated by subtracting the date of birth from the date when the panoramic radiograph was taken. The radiographs were taken for diagnostic purposes and none of the children had undergone orthodontic treatment before taking the selected radiograph. Only children who were free of anomalies and pathologies were selected. The socioeconomic background of children in the modern sample can be described as middle-tolow, since the residency dental clinics provide lower cost services in comparison with the private clinics. The age and sex distribution of each sample is shown in Table 1. Values are in number of individuals.

The two samples represent an important environmental transition in Portugal, with its critical turning point roughly between 1960 and 1980. Although spanning several decades, children in the historic sample symbolize a population who was going through tremendous social and economic difficulties and where changes were occurring at an unbearable slow rate. Portugal remained a very isolated and underdeveloped society for most of the 20th century. The rise of a 50-year long dictatorship established a strong and repressive state which reinforced the closed economic and social nature of the country. Portuguese per capita income was one of the lowest in Europe and living conditions were very poor until quite recently. Children in the modern sample, on the other hand, represent a major change towards improved living conditions for the all population, but for children in particular. In 1974 a military coup overthrew the dictatorship and set the basis for a democratic pluralistic system in Portugal [START_REF] Baiôa | The political history of twentieth-century Portugal[END_REF] that accomplished major improvements in economic and social welfare.

Portugal experienced the first significant economic changes in 1960 with the country's union with the EFTA (European Free Trade Association) [START_REF] Corkill | Aspects of Portugal's economic development during the late Estado Novo[END_REF]. Per capita income doubled and tripled in just a few decades and initiated the exponential growth of the economy [START_REF] Tortella | Patterns of economic retardation and recovery in southwestern Europe in the nineteenth and twentieth centuries[END_REF]. In parallel with the increase in per capita income is the twofold increase in public expenditures on health and in social security coverage [START_REF] Lobo | Portugal na Europa, 1960-1999: Uma leitura política da convergência económica[END_REF]. In addition, the dictatorship years created an absent welfare state and it was not until the 1970s that public health and social welfare programs were established and later successfully implemented [START_REF] Veiga | Social changes and better health conditions of the Portuguese population 1974-2000[END_REF]. Health conditions in Portugal were long among the poorest in Western Europe and it was only between 1970 and 1990 that the greatest relative declines in both infant and post-neonatal mortality occurred [START_REF] Barreto | A situação económica em Portugal, 1960-1999[END_REF]. Rapid changes are also expressed in dietary improvements since 1960-1980, namely increased per capita total daily caloric intakes and percentage of daily caloric intake from animal products, such as milk or meat [START_REF] Cardoso | Secular changes in body height and weight of Portuguese boys over one century[END_REF].

Our analysis assumes that both samples do not differ genetically and any differences detected in dental root formation are likely to derive from environmental influences. Portugal has remained very genetically homogenous [START_REF] Pereira | Diversity of mtDNA lineages in Portugal: not a genetic edge of European variation[END_REF], where foreign immigration is unlikely to have played an important role behind the changes in tooth formation. For example, [START_REF] Pereira | Diversity of mtDNA lineages in Portugal: not a genetic edge of European variation[END_REF] examined the diversity in mtDNA of the modern Portuguese population by comparing Northern, Central, and Southern Portugal and did not detect a statistically significant difference between the three regions. Similarly, a study using the Y-chromosome found with no statistically significant differences among the three regions (Beleza et al., 2006). In addition, any genetic contribution to the difference in dental root formation between the historic and modern samples is not possible to assess given that there is no known basis for the genetic determination of tooth formation differences between populations. This is supported by various recent studies, where it is shown that differences in tooth formation timing does not seem to depend predominantly on population differences [START_REF] Braga | Non-adult dental age assessment: correspondence analysis and linear regression versus Bayesian predictions[END_REF][START_REF] Liversidge | Growth of permanent mandibular teeth of British children aged 4 to 9 years[END_REF][START_REF] Liversidge | Variation in modern human dental development[END_REF][START_REF] Liversidge | Timing of Demirjian tooth formation stages[END_REF][START_REF] Maber | Accuracy of age estimation of radiographic methods using developing teeth[END_REF]. This is further supported by the histological findings provided by [START_REF] Reid | Variation in modern human enamel formation times[END_REF] and [START_REF] Reid | Variation in modern human premolar enamel formation times: Implications for Neandertals[END_REF], who have found that population differences in crown formation timing are remarkably small, particularly for molars.

Data collection

The maturation of seven developing permanent teeth (excluding M3) in the mandible was assessed using Demirjian's eight stages [START_REF] Demirjian | A new system of dental age assessment[END_REF]. Stages were rated from radiographs in both the historic and modern samples, but the Lisbon collection data also includes stages rated from direct observations of loose teeth. There were some missing teeth in the historic sample and, hence, sample size for each tooth varies slightly in this sample.

Because of the limitations associated with the age at which the children were radiographed in the modern sample, only the later stages of tooth formation, namely root formation, are included in this study. While the age of 6 was imposed as the lower limit of the samples' age range because of constraints of the modern sample, 18 years was set as the upper limit because it is the age at which the entire dentition (except M3) is fully formed in both samples. Data on Demirjian's staging was collected from the Lisbon sample (historic) by author H.C., from the Coimbra sample (historic) by Y.H. and from the Porto sample (modern) by P.J.

Assigning a categorical system to the continuous process of dental maturation includes problems of defining stages and subjectivity in identifying consecutive stages. Although the stages devised by [START_REF] Demirjian | A new system of dental age assessment[END_REF] probably comprise the most carefully defined system, based on radiographic pictures, diagrams and written criteria, it is essential to assess reliability of stage rating by conducting intra-and interobserver tests. Intra-individual repeatability and interindividual reproducibility were assessed using Cohen's Kappa and percent of agreement performed on double ratings of a subset of 28 orthopantomograms. Sign tests were used to assess whether the intra-or interobserver difference in scores was zero or equally likely to be positive (overscoring) or negative (underscoring). Intra-and interobserver agreement range from substantial to almost perfect agreement [START_REF] Landis | The measurement of observer agreement for categorical data[END_REF] (Table 2) and are consistent with reports in the literature [START_REF] Dhanjal | Reproducibility of radiographic stage assessment of third molars[END_REF][START_REF] Levesque | The inter-examiner variation in rating dental formation from radiographs[END_REF][START_REF] Leurs | Dental age in Dutch children[END_REF][START_REF] Liversidge | Timing of Demirjian tooth formation stages[END_REF][START_REF] Maber | Accuracy of age estimation of radiographic methods using developing teeth[END_REF][START_REF] Nykänen | Validity of the Demirjian method for dental age estimation when applied to Norwegian children[END_REF]. Sign tests do not show any systematic errors in intra-or inter-observer assessment. The difference between two scores did not exceed one stage for any tooth and sign tests showed that one observer was not systematically underscoring or overscoring relative to the other observer.

Assessing secular change

Dental maturation data was dichotomized into "stage not-attained" versus "stage attained" and the median age-of-attainment of root stages of individual teeth was calculated for each sample and sex separately, using a cumulative distribution function. At first, an exploratory analysis of the data was carried out and scatter-plots were visually inspected for outliers. Standardized residuals and Cook's distances were calculated for each observation, for detection of outliers and influential cases, respectively. Observations with standardized residuals greater than 3 in absolute value were excluded, as well as observations with a Cook's distance greater than one. Three outliers were detected in the historic sample and 15 in the modern sample. These markedly deviated observations represent spurious data which resulted from observation and transcription errors during data collection. The median age-of-attainment of a stage was calculated using logistic regression and is equivalent to the age when half the children (the median or the 50th percentile) reach or attain that stage [START_REF] Liversidge | Dental age revisited[END_REF]. The median ageof-attainment has also been described as mean age-of-attainment [START_REF] Liversidge | Timing of Demirjian tooth formation stages[END_REF][START_REF] Liversidge | Dental age revisited[END_REF], but is different from what has been called mean age at a stage, where the ages of children at a certain stage are averaged [START_REF] Nadler | Earlier dental maturation: fact or fiction?[END_REF]. In addition to the median, the lower quartile (LQ, 25 th percentile), upper quartile (UQ, 75 th percentile) and the inter-quartile range (IQR) were also calculated to provide a measure of variability around the median. The median and quartiles were obtained from the logistic regression formulae and not directly from the sample distribution. The significance of differences in median age-of-attainment between samples was obtained by calculating an overall logistic regression model for each sex alone, where sample (historic versus modern) is treated as categorical covariate, and testing whether the coefficient for the variable "sample" is statistically different from zero (no statistically significant differences), using the Wald statistic. The use of logistic regression overcomes the difficulties of non-normality or heterocedasticity for the predictor variable [START_REF] Pampel | Logistic regression: a primer[END_REF][START_REF] Wright | Logistic regression[END_REF], as well as of an uneven age distribution and inadequate age range that hamper a number of studies on dental development [START_REF] Liversidge | Variation in crown and root formation and eruption of human deciduous teeth[END_REF][START_REF] Liversidge | Dental age revisited[END_REF][START_REF] Smith | Standards of human tooth formation and dental age assessment[END_REF]. In addition, the logistic regression approach is particularly appropriate for the last stage (H), because as it persists for an individual's whole life, timing cannot be estimated from other methods, such as mean age at that stage [START_REF] Liversidge | Dental age revisited[END_REF]. The -2 Log Likelihood and the Hosmer and Lemeshow test were used to assess the quality of the logistic regression model adjusted to the data of each individual tooth stage. The significance of logistic regression coefficients was tested using the Wald statistic. Logistic regression models which fitted the data poorly and provided statistically insignificant coefficients for the constant and predictor variable (age) were not considered.

Differences in median age-of-attainment between consecutive stages (interval between stages) and between the earliest and latest stages observed for the root were calculated in both sexes, to assess changes in the duration of tooth (root) formation between the modern and historic samples. Wilcoxon matched pairs test was used to test the significance of differences in median age-of-attainment between stages in the modern and historic samples. Differences in median age-of-attainment between consecutive stages of male and female teeth were also compared using a Mann-Whitney test. This was carried out to assess sex differences in the duration of tooth formation.

Assessing mortality bias

The analysis of the effects of cause of death, to disentangle the influence of mortality bias, is rooted on the assertion that the health conditions which lead to a child's death are likely to influence his or her growth status: natural causes are likely to have an effect, accidental causes are not. Our assumption is that children who have died from an accident (e.g. drowning, fall, road accident) have a greater probability of most closely resembling their living counterparts, as their developmental status is not compromised by their health status which eventually determined their premature death. Since there is reliable information about cause of death in the historic sample, as obtained from the civil registration of death, we divided it into two distinct groups: one of children who died of natural causes (n = 68) and one of children who died of accidental violent deaths (n = 13). We then estimated dental age in both groups and compared it to chronological age in order to assess whether dental development in the group of children who died accidentally falls ahead that in the group of children who died of natural cases.

For each child in the historic sample, dental age was estimated for each individual tooth using the sex specific median age-of-attainment calculated from the modern sample and a mean age for each child was calculated from the ages obtained from each individual tooth. By doing this we make the general assumption that the child was average and that each group of children (natural versus accidental causes) represent the average of their group. Age estimation from mean age-of-attainment has been deemed appropriate for comparative purposes [START_REF] Liversidge | Dental age revisited[END_REF], such as in this case where the same approach is being applied to the two groups being compared. A measure of relative development was calculated by subtracting the chronological age from the estimated dental age and the sexes were pooled. Mean differences between dental and chronological age in each group were compared using a t-test to determine whether dental development is significantly delayed in the natural deaths group relative to the accidental deaths group. Although the groups have a very different sample size, the t-test is considered a robust test, particularly when the variances are similar in the two groups (Zar, 1999), such as in this case. If there are no statistically significant differences in mean discrepancies between the two groups, then one group is not significantly delayed or advanced relative to the other in dental development and a premature death effect is not detected. Owing to the small sample size of the group of children who died of accidental violent deaths, a power analysis was also performed to assess the probability of making a type II error (Zar, 1999). Since we are concerned with whether the differences between groups can explain the difference between the historic and modern samples, we are only interested with a power analysis for a test which can detect a difference between groups of the magnitude of the difference between the historic and modern samples.

RESULTS

Secular change

In both sexes, all individual root stages show earlier median ages-of-attainment in the modern sample, showing that timing of formation is significantly advanced in the modern compared to the historic sample (Tables 3and 4). Advancement in median age-of-attainment in the modern sample relative to the historic sample ranged between 0.19 and 1.98 years (mean = 1.22 years) in boys and between 0.59 and 2.14 years in girls (mean = 1.47 years). However, not all historic-modern comparisons showed statistically significant differences (P < 0.05).

The exceptions are: the canine (stage G), the first premolar (stages E and H), and the second molar (stages E and G) in boys; and the first premolar (stage G) in girls. Figure 1 illustrates secular acceleration in dental root maturation, by showing the mean advancement in formation timing of dental stages E through H of the second premolar in girls. The age-of-attainment of root developmental stages was earlier in girls, except in the first incisor (stage G) in the modern and historic samples, and the first premolar (stage H), first molar (stage G) and second molar (stage G) in the historic sample (Tables 3 and4). This indicates that girls begin to develop their teeth earlier than boys, and the mean sex difference in timing is about one half year, both in the historic and modern samples. Tables 5 and6 show that the mean age interval between consecutive root stages, and between the earliest and latest stages observed are similar in both the modern and historic samples. For example, in girls, the mean duration of formation of a single stage (F-L column) in the historic sample (1.87 years) is very similar to that of the modern sample (1.98 years). When comparing secular differences in duration of stage formation, only data which could be paired (modern and historic) were used to calculate the Wicoxon tests. This test did not show significant differences between the modern and historic samples in the duration of formation of individual stages, in either boys or girls.

-N F-L O-N F-L C F -2.44 -4.40 -3.37 -4.59 G -1.96 - -1.22 - H - - - - P1 E -2.69 -4.78 -1.00 -4.75 F - - b - G - - b - H - - - - P2 E - - b b F - -3.52 b -4.08 G - - b - H - - - - M1 G -3.56 -3.56 -2.78 -2.78 Tooth a Stage Historic Modern O-N F-L O-N F-L H - - - - M2 E - -7.32 b -6.04 F - - b - G -3.69 - -2.45 - H - - - - Mean -2.87 -4.72 -2.16 -4.45
The incisors are not shown due to incomplete data in girls. a I1, central incisor; I2 lateral incisor; C, canine; PM1, first premolar; PM2, second premolar; M1, first molar; M2, second molar. b Denotes missing data for historic sample, which has also been omitted in the modern sample for comparative purposes.

In only a few teeth (second premolar in girls, and first premolar and second molar in boys) was it possible to determine the length of time required for the formation of tooth roots, obtained as the mean time interval between initial calcification (stage E) and the root completed stage (stage H). No significant differences were found between the modern and historic samples in duration of complete root formation. For example, the length of time required for the formation of the root of the first premolar in boys was 4.78 years in the historic sample and 4.75 years in the modern sample. Second premolar root formation time in girls was 5.04 in the historic sample and 5.08 in the modern sample.

There is also a tendency for a greater mean age interval between consecutive stages in boys (historic and modern), compared with that of girls. This suggests that girls advance more rapidly in root formation. The Mann-Whitney tests shows that sex differences in the duration of tooth formation are only significant in the historic sample (df = 17, P = 0.0275).

Mortality bias

Dental ages were estimated in the historic sample and the mean difference between dental and chronological age in the group of children who died of natural causes is -2.44 years (s.d. = 1.36), whereas the same difference is -2.66 years (s.d. = 1.25) for the group of children who died of accidental causes. A t-test failed to show statistically significant differences between the two groups (P = 0.570), thus suggesting that mortality bias has no noteworthy effect on root formation of the historic sample. The power analysis performed showed that the probability of making a Type II error when detecting a difference between the groups of 1.22 and 1.47 years (mean difference between the historic and modern samples for boys and girls) is 0.76 and 0.96, respectively. Therefore, the probability of accepting the null hypothesis of no differences between groups, when it is false, is between 0.24 and 0.04.

DISCUSSION

This study demonstrates a consistent secular acceleration in tooth formation timing, namely in the timing of root formation. We were able to show a statistically significant advancement in timing of dental maturation of Portuguese boys and girls over the last half a century. Results also suggest that an earlier timing of dental maturation was not accompanied by a change in the duration of root formation. Therefore, these results suggest that secular change is altering the age at which dentine starts to form and not how fast it is forming.

While other studies have suggested a secular acceleration in dental maturation [START_REF] Holtgrave | Acceleration in dental development: fact or fiction[END_REF][START_REF] Monge | Dental calcification stages of the permanent M1 and M2 in U.S. children of African American and European American ancestry born in the 1990s[END_REF], this was accomplished by comparing a sample of modern children with earlier dental development standards. To the best of our knowledge, the only exception is the research carried out by [START_REF] Simpson | A radiographic study of the development of the human mandibular dentition[END_REF], where dental development in two samples of American children, ∼50 years a part, have been compared using suitable statistical techniques. In their study, a slight delay in root formation of the mandibular canine was noted in the earlier sample. Results shown here agree with the findings of [START_REF] Heuzé | Testing the quality of nonadult Bayesian dental age assessment methods to juvenile skeletal remains: the Lisbon collection children and secular trend effects[END_REF], who showed that a Bayesian nongeographic-specific dental age estimation method, based on a diverse sample of modern children, consistently underestimated the age of a sample of children from the Lisbon collection by about one year.

Our results are also consistent with the histological findings of [START_REF] Reid | Variation in modern human enamel formation times[END_REF] and [START_REF] Reid | Variation in modern human premolar enamel formation times: Implications for Neandertals[END_REF], who have shown that duration of crown formation has not changed over time. This leaves (1) a change in the timing of initiation or (2) a change in the rate or duration of dentinogenesis, to explain a secular acceleration in tooth maturation. A change in timing over time is precisely what we have found, together with an unchanged duration of root formation. In addition, results indicate that girls not only begin to develop their teeth earlier than boys, but also advance through root stages more rapidly (both historic and modern samples), comparing favorably with results reported by Demirjan and Levesque (1980).

Although mortality bias was an initial concern, analysis presented here shows that root formation in the group of children who died of natural causes is not significantly delayed relative to root formation in the group of children who died from accidents. This was confirmed by the power analysis performed in this study, which showed that there is a relatively low probability of assuming that the groups of children did not differed, when in fact they may have been different. There are only two ways of increasing the power of a test, and one is out of our reach (increasing sample size). We may, however, increase the power by changing the nature of the test (Sokal and Rolf, 1995), namely utilizing a nonparametric Mann-Whitney test. The significance of this test is roughly similar to that of the t-test (P = 0.598) obtained. If we assume that the death of children in the accidental deaths group cannot reflect the effects of their health status at the time of their death, their similarity with the children who died of natural causes supports the assertion that there is no significant effect of premature death on the developmental status of children in the historic sample. Although we cannot ignore that the Lisbon and Coimbra children are dead and died at a relatively earlier age than the modern children will eventually die, ultimately, the historic children died at a relatively earlier age because they had a worst environment. Therefore, the historic sample simply reflects a delayed growth as a consequence of the poor environment in which they lived and the comparison between the historic and modern sample is likely to reflect a fundamental change in the environment, which promoted better growth and a secular acceleration in development of the modern sample.

One of this study's limitations is the small size of the historic sample and its possible insufficient age range, which may account for earlier maturation in one or a few individual tooth stages. This may also help to explain why the earlier timing of dental development in the modern sample was not statistically significant for all individual tooth stages analyzed. However, it is unlikely that the small sample size can explain such a consistent pattern of dental delay in the historic sample, across the entire permanent dentition. Although the historic sample is relatively small, its importance lies in being representative of the modern sample at an early period, when radiographs or other sources of information about dental development of children are typically unavailable, at least in Portugal. The logistic regression approach used in this study accounts for the variation of development time of individual tooth stages and for variation which results from random fluctuations in the small historic sample.

In addition, the sexes were treated separately so that what appears to be accelerated or delayed development cannot be accounted by sex differences in growth. The cross-sectional nature of the sample may also be deemed inappropriate to assess changes in duration of root formation, but results also show a consistent pattern across the whole dentition.

Although we have been able to demonstrate a secular acceleration towards earlier root formation in Portuguese children, what exactly it is that might underlie this secular trend in tooth development? The mechanism by which teeth mature earlier is unknown, but nutrition may play a significant role in such trend. In particular, nutrition may change the age at initiation of root formation. Although results are not conclusive, a few studies have examined the influence of nutrition on dental maturation. For example, Rai (2009) using third molars extracted from a sample of North Indian patients between the ages of 17 and 21, found that dental and chronological age did not differ in the group of well nourished individuals, but dental age underestimated chronological age in the group of malnourished subjects. In this study, the patients were categorized according to the nutritional risk index, which incorporates information about the subject's weight and plasma albumin level [START_REF] Rai | Effect of nutrition on coronal displacement of cementum in impacted teeth[END_REF]. A significant effect of malnutrition on dental development is strongly suggested by Murchinson et al. (1988) in an experimental study carried out with protein-deprived infant rhesus monkeys. Crown-root length in protein restricted monkeys was found to be significantly less than those of controls, but only for deciduous second molars. [START_REF] Hilgers | Childhood obesity and dental development[END_REF] 2007) did not find a significant delay in tooth growth of stunted Peruvian children between the ages of 9.5 and 16.5.

Despite the conflicting results about the effects of nutrition on dental maturation of modern children, one of the primary explanations behind the secular trend phenomena is nutritional, involving an increase in calories, quality of diet, increased availability of certain foods and decrease in energy loss and expenditure, which accelerate somatic maturation timing [START_REF] Bogin | Patterns of human growth[END_REF][START_REF] Garn | The Secular trend in size and maturational timing and its implications for nutritional assessment[END_REF][START_REF] Malina | Research on secular trends in auxology[END_REF][START_REF] Susanne | Living conditions and secular trend[END_REF][START_REF] Tanner | Fetus into Man: Physical Growth from Conception to Maturity[END_REF]. The acceleration in dental root maturation timing of the Portuguese detected in this study, correlates well with a period of great political, social and economic changes initiated in Portugal in the 1960s and 1970s, which had critical consequences for the physical development of children, through access to better nutrition, especially more protein and caloric intake during infancy, but also through greater overall sanitary conditions and hygiene, lessening of disease, as well as delivery of social and medical care. While the historic sample reflects a period of less development during the 20th century, the children in the modern sample were all born after 1970 and represent a period of great changes towards modernization and improved environmental conditions. The improved environment for human growth allowed for greater growth in height and weight of Portuguese children [START_REF] Cardoso | Secular changes in body height and weight of Portuguese boys over one century[END_REF], as well as for a decrease in age of menarche [START_REF] Padez | Social background and age at menarche in Portuguese university students: a note on the secular changes in Portugal[END_REF]. These changes in body size and earlier maturation of the Portuguese ad to the widely documented secular trends that are taking place in the industrialized nations of the world (see [START_REF] Hauspie | Secular changes in growth[END_REF]Bodzsar and[START_REF] Bodzsar | Secular growth change in Europe[END_REF], for a review). Temporal changes in height, weight and age at menarche have documented the great plasticity of the human growth process [START_REF] Bogin | Patterns of human growth[END_REF], and now dental maturation.

Although environmental factors have been somewhat neglected as sources of variation in dental development, our results show that differences in timing of root stages of individual teeth between the modern and historic samples can be ascribed to a secular advancement in dental development of about 1-1.5 years. This secular trend effect has important consequences for a wide variety of research areas. For example, these results have an impact on medical clinical practice, by suggesting that earlier dental age standards may not be appropriate for orthodontic treatment of modern patients in the developed nations. In a forensic context, since children from developing countries mimic children from developed countries in earlier periods of time, dental age estimation methods based on children of the developed world may not perform well in undocumented refugee children and young illegal immigrants from the developing nations. Results also suggest that the variability of dental formation timing encountered in other Hominids and Hominins species should be more carefully interpreted since this variability could result from differences in environmental quality more than from genetic differences. Yet, future research is still needed to substantiate the findings in this study, particularly with respect to changes in the timing of enamel formation and to changes in the rate of tooth formation. Additionally, it is also interesting to explore further whether accelerated maturation is associated with advanced emergence.

CONCLUSION

The results in this study confirm previous work and show that the children in the modern sample are consistently advanced in timing of root maturation, compared to children in the historic sample, but they do not seem to differ in duration of root formation. The detection of a secular acceleration in dental maturation is particularly important because it provides an important additional insight into the link between human growth and the environment. In fact, this study shows that the plasticity in dental maturation is greater than previously thought. The acceleration in dental maturation detected here seems to reflect a greater access to better nutrition, lessening of disease, decrease in energy expenditure and improvement in overall living conditions experienced by modern Portuguese children, as a consequence of major political, economical, social and public health changes which occurred in Portugal at the late 20th century.

obtain additional biographic information for the children in the Coimbra collection; to Dr. Américo Afonso, Dr. José António and Dr. Inês Caldas, for support during data collection at the Faculty of Dentistry in Porto; to Dr. Joan T. Richtsmeier for her editorial suggestions; to Dr. Janet Monge for re-prints; and to Carolan Wood for facilitating the access to important bibliographic sources. The two anonymous reviewers provided crucial comments which improved the paper significantly.

Figure 1 .

 1 Figure 1. Median secular advancement (in years) in formation timing of dental root stages E through H, of the second premolar in girls. The smoothed cumulative frequency distribution curves (logistic regression) for stages E through H, of the second premolar in girls, are depicted. The solid line corresponds to the historic data and the dashed line to the modern data.

Table 1 .

 1 Age and sex distribution of the historic and modern samples

Age (years) Historic Modern Girls Boys Girls Boys

	Age (years)	Historic		Modern
		Girls	Boys	Girls	Boys
	13.0-13.9	4	3	24	28
	14.0-14.9	5	5	21	13
	15.0-15.9	8	6	15	5
	16.0-16.9	2	3	10	10
	17.0-17.9	1	5	12	6
	18.0-18.9	4	2	6	6
	Total	60	54	260	261
	6.0-6.9	3	4	16
	7.0-7.9	5	4	20
	8.0-8.9	4	5	34
	9.0-9.9	5	3	36
	10.0-10.9	9	5	27
	11.0-11.9	5	5	15
	12.0-12.9	5	4	24

Table 2 .

 2 Cohen's Kappa and percentage of agreement (in parentheses) for intra-observer replicability and inter-observer reproducibility in double ratings of 28 orthopantomograms

		Replicability		Reproducibility
			Observer 1	Observer 2	Observer 3
	Observer 1	0.84 (88%)	-
	Observer 2	0.64 (73%)	0.64 (73%)	-
	Observer 3	0.87 (93%)	0.63 (85%)	0.75 (82%)	-

Table 3 .

 3 Median age-of-attainment in years (M) for each individual tooth stage in girls, and difference (Diff) in age-of-attainment between historic and modern samples

	Tooth a Stage		Historic			Modern		Diff	Sign
			LQ	M	UQ	IQR	LQ	M	UQ	IQR
	I1	G	7.78	8.55	9.31	1.53	6.49	6.70	6.91	0.42	1.85	0.003
		H	-	-	-	-	6.98	7.37	7.75	0.76	-	-
	I2	G	8.12	8.60	9.08	0.97	7.07	7.43	7.78	0.71	1.17	0.002
		H	-	-	-	-	7.48	8.18	8.87	1.39	-	-
	C	F	8.19	8.61	9.03	0.84	6.49	6.83	7.18	0.69	1.78	0.000
		G	10.46	10.83	11.19	0.73	9.41	9.99	10.57	1.16	0.84	0.015
		H	11.22	11.93	12.64	1.42	10.46	11.10	11.73	1.28	0.83	0.048
	P1	E	-	-	-		6.63	6.91	7.20	0.57	-	-
		F	9.38	9.84	10.31	0.93	7.49	7.97	8.46	0.98	1.87	0.000
		G	10.51	11.04	11.57	1.06	9.92	10.45	10.97	1.06	0.59	0.095
		H	12.07	12.96	13.85	1.78	10.83	11.52	12.20	1.37	1.44	0.002
	P2	E	8.63	9.17	9.71	1.08	6.84	7.40	7.96	1.12	1.77	0.000
		F	10.35	10.82	11.29	0.94	7.91	8.68	9.45	1.53	2.14	0.000
		G	11.84	12.82	13.80	1.96	10.52	11.20	11.87	1.35	1.62	0.001
		H	13.04	14.21	15.39	2.36	11.82	12.48	13.15	1.33	1.73	0.000
	M1	G	7.27	8.08	8.89	1.62	6.32	6.65	6.98	0.66	1.43	0.001

Table 4 .

 4 Median age-of-attainment in years (M) for each individual tooth stage in boys, and difference (Diff) in age-of-attainment between historic and modern samples

	Tooth a Stage		Historic			Modern		Diff	Sign
			LQ	M	UQ	IQR	LQ	M	UQ	IQR
	I1	G	7.85	8.41	8.97	1.12	5.67	6.50	7.33	1.65	1.91	0.003
		H	8.51	9.51	10.51	2.00	7.63	8.12	8.61	0.98	1.39	0.003
	I2	G	8.93	9.34	9.76	0.83	7.50	7.99	8.49	1.00	1.35	0.002
		H	9.97	10.24	10.50	0.53	8.51	8.97	9.43	0.92	1.27	0.002
	C	F	8.49	9.34	10.19	1.70	7.12	7.79	8.46	1.34	1.55	0.001
		G	11.14	11.78	12.43	1.29	10.43	11.16	11.88	1.44	0.62	0.132
		H	12.63	13.74	14.85	2.22	11.71	12.38	13.04	1.33	1.36	0.006
	P1	E	7.45	7.77	8.09	0.65	7.01	7.58	8.16	1.15	0.19	0.687
		F	9.97	10.46	10.94	0.96	8.13	8.58	9.03	0.90	1.88	0.000

Table 5 .

 5 Differences between median age-of-attainment in years of one individual tooth stage and the next (O-N) and of the first and last stages observed (F-L), in girls Denotes missing data for historic sample, which has also been omitted in the modern sample for comparative purposes.

	Tooth a	Stage	Historic		Modern
			O-N	F-L	O-N	F-L
	C	F	-2.22	-3.32	-3.16	-4.27
		G	-1.10	-	-1.11	-
		H	-	-	-	-
	P1	E	-	-	b	b
		F	-1.20	-3.12	-2.48	-3.55
		G	-1.92	-	-1.07	-
		H	-	-	-	-
	P2	E	-1.65	-5.04	-1.28	-5.08
		F	-2.00	-	-2.52	-
		G	-1.39	-	-1.28	-
		H	-	-	-	-
	M1	G	-2.52	-2.52	-2.27	-2.27
		H	-	-	-	-
	M2	E	-	-	b	b
		F	-1.71	-4.70	-1.37	-4.66
		G	-2.99	-	-3.29	-
		H	-	-	-	-

b

Table 6 .

 6 Differences between median age-of-attainment in years of one individual tooth stage and the next (O-N) and of the first and last stages observed (F-L), in boys

	Tooth a	Stage	Historic	Modern
		O

  also found a significant effect of nutrition on dental development, but in conditions of overnutrition. BMI status was determined in a sample of children between the ages of 8 and 15, where a mean dental age acceleration of 1.53 years was found for obese individuals, compared to 0.68 years for normal children. Comparatively,[START_REF] Flores-Mir | Association between growth stunting with dental development and skeletal maturation stage[END_REF] andCameriere et al. (

Acknowledgements

The authors are grateful to Dr. Barry Bogin for important insights and for his comments on an earlier version of this article; to Dr. Marina Andrade for statistical advice; to Dr. Helen Liversidge for important suggestions; to Dr. Ana Luísa Santos, whose diligence allowed us to

Contract grant sponsor: Fundaçaõ para a Ciência e Tecnologia; Contract grant number: SFRH/BPD/22142/2005; Contract grant sponsor: Public Health Service; Contract grant numbers: R01 DE016886, CDC 5R01 DD000350; Contract grant sponsor: The Foundation Fyssen.

Zar JH, 1999. Biostatistical analysis. New Jersey: Prentice Hall. 960 p.


David Bramoullé

Trade relations between Sicily, Ifrīqiya and Egypt under the Fatimids and Zirids of Ifrīqiya (10 th -11 st centuries), in

p.93

"The situation is worthening all the time. People are very worried about what's going on in Sicily and the fact that the enemy mastered most of it and because here the food prices levelled high because the city is dependent upon Sicily for its food ". 1 The 18 th of August 1061, Labrāṭ b. Moses b. Sughmār, the Jewish judge (dayyan) of Mahdiya, the main maritime town on the coasts of Ifrīqiya (approximately modern Tunisia, east of Algeria and west of Libya), shared his concerns with his interlocutor and business partner in Egypt, (p. 94) Nahray b. Nissīm, waiting for news and goods from Ifrīqiya and Sicily. This letter, quite a long one in fact, and many others bear witness to the strong ties between Sicily and North Africa. It even attests to the growing dependence which has gradually established in Ifrīqiya with regard to Sicilian agriculture productions about which Ibn Ḥawqal, passing through the island int the 970's, did not pay much attention to. Despite the obvious exaggerations he expressed towards Sicily and its people who found no grace in his sight, it is also true than in a century the context had changed. 2 Since the first days of the Aghlabid conquest of the island in 827, a conquest about which sources suggest that it followed regular commercial traffic between Ifrīqiya and Sicily, relations between the two territories, now united under the same authority, seem to have intensified. 3 In 909-910, the Fatimids overthrow of the Aghlabid emirs confirmed this.

From 910, the conquest of Ifrīqiya and Sicily by the Fatimid caliphs placed the two territories in a situation of increasing economic and political interdependence. If the union of Sicily and Ifrīqiya under a common Muslim tutelage predates the Fatimids, the sources show how much, from the 10 th century onward, the commercial relations between the Ifrīqiyan ports and those of Sicily became more pronounced. Beyond mere trade, the island played a central ideological role for the Ismaili caliphs of Ifrīqiya. Engaged in an ideological war against their Islamic competitors, the Abbassids caliphs of Baghdad and the Umayyads of Cordoba, both Sunnis, the Ismailis Fatimids had to prove the Islamic world their legitimacy as the sole 1 INA D 55 No 13, recto l. 42, margin ll.1-4. In Moshe Gil, ed. In the Kingdom of Ishmael, (Jerusalem:

contender to the caliphal throne. The best way to do it was to defeat the Christians, especially the Byzantines, usually called the Rums in Arabic sources and considered as the epitome of the enemies of the Islamic world since the 7 th century, on their own "field"; the Mediterranean called the sea of the Romans (baḥr al-rūm) in most Arabic sources. On this aspect, Sicily was of some interest for the Fatimids. A part of the island was still on the hands of the Byzantine when the Fatimid took over the power in Ifrīqiya and decided to come to take what they considered as their due in Aghlabid Sicily. To outstrip the Aghlabids (p. 95) in the control of this territory, the island became a main goal for the Fatimids between 910 and 973 while during the same period the Abbassids were defeated by the Byzantine in northern Syria and the Umayyads were negotiating agreements with Constantinople against the Fatimids. 4 Because of its natural resources and its location near Southern Italia, Sicily also played a major role in Fatimid sea policy against these same Byzantines. Sicily thus furnished a tactical advantage with both a practical and ideological aspect: a naval base for commerce and defense set in the center of the Mediterranean, it could also function as the lynchpin in a narrative meant to legitimize Fatimid claims to the caliphate.

Sicily's importance in the Fatimid strategy did not diminish, even after their departure to Egypt in 973 and the establishment of the government of the Zirid emirs of Ifrīqiya and the Kalbids in Sicily, both of them under Egyptian's theoretical authority, the role of the island in the Fatimid strategy did not get weaker. On the contrary, both the Arabic documentation of the 10 th and 11 th centuries, such as geographic treaties and the Islamic juridic texts -the fatwas-and the very rich letters of the Geniza from the 11 th and 12 th centuries testify that the island, blessed by varied agricultural productions, played a major role in supplying not only Ifrīqiya, but also Fatimid Egypt. Moreover, in Palermo, Kalbid emirs favored the emergence of quality craftsmanship which strengthened the role of the island and made it an obligatory space for exchanges between Egypt and Ifrīqiya but also more largely between the Muslim and Christian worlds, and the gradual conquest of the island by the Normans in the second half of the 11 th century did not fundamentally change things.

RENOWNED AND EXPORTED PRODUCTIONS FROM SICILY

Far from the portrait drawn up in the 970's by Ibn Ḥawqal who reported that the vital interests of the Sicilians depended on importers, agricultural and artisanal productions were numerous and gave rise to renowned exports. 5 The export of food products to Ifrīqiya is documented as early as the 10 th century, when the Fatimids were still there and even before during the Aghlabid era. While the early documentation does not say anything (p. 96) about the food products from Sicily, medieval geographers, fatwas, and Geniza letters, written mainly after 1020, furnish details regarding this agricultural production. Much of this was cereal cultivation, mainly barley and wheat concerning which al-Idrīsī attests that at least by Norman times, vermicelli (iṭrīya) was made near a place called Trabia and exported in all directions. [START_REF] Bramoullé | Nuzhat al-mushtaq fī ikhtiraq al-āfāq[END_REF] Exportation of wheat to Ifrīqiya and Egypt appears in several fatwas by the Muslim jurist al-Qābisī (d. 1012) and letters from the 11 th century. [START_REF] Al-Wansharīsī | yār al-mu'rib wa-al-jāmi' al-mughrib 'an fatāwī ahl Ifrīqiyya wa-al-Andalus wa-al-Maghrib[END_REF] In several fatwas by al-Māzarī (d. 1141), rental contracts for the transportation of Sicilian wheat to Ifrīqiya were signed on a regular basis until the beginning of the 12 th century, when the Sunni jurists of Ifrīqiya forbade trade with an enemy land as Sicily was considered by that time. 8 Syracuse is clearly mentioned as a port where big ships were loading wheat in the 12 th century 9 . Rice is also mentioned in this documentation, albeit in a more anecdotal way. In a letter from Mazara written between 1053 and 1060, the writer refers to sending rice to Egypt. It is unclear, however, whether this is a reference to local rice or not. 10 The Muslim conquest also made it possible to introduce or develop a number of new vegetable products thanks to the importation of new agrarian techniques. Sugar cane, introduced in the region of Palermo and mentioned for the first time around 930, spread throughout the island. 11 The kitchens of the Fatimids, which produced large quantities of pastries, needed a great deal of sugar. The caliphs had cane plantations on the island, and sugar for candy figures among Sicilian exports in the 10 th century. 12 (p. 97)

The orchards and the fruits of Sicily are abundantly referred to in medieval literature. [START_REF] Ḥawqal | [END_REF] Citrus fruits enjoyed a great reputation throughout the Mediterranean, and beverages were made with cane sugar and exported along with wine. 14 Shelled almonds and nuts of all kinds were also widely exported Sicilian products. 15 The breeding of animals such as cows allowed the manufacture of a very famous cheese appreciated everywhere as well as the development of a leather industry. 16 Craft leather from Syracuse is cited, and shipments of hundreds of calfskins, deerskins, and hides of other types appear in the texts along with wax and honey. 17 Sicily was also famous for its fishing activity. Ibn Ḥawqal writes that the fisheries of Sicily were leased, and al-Idrīsī is more precise by indicating that fishing for tuna, swordfish, and shad was practiced in Trapani, Termini, Caronia, Oliveri, and Milazzo (Figure 1). 18 In Salso, geographers refer to the importance of fishing activity and the succulent taste of the fish. In Lentini, the river full of fish favored an important fishing activity. These fish were exported widely. 19 Archaeological documentation attests that the salted fish from Sicily were exported to Ifrīqiya and probably also to Provence as analysis of ceramic jars from this period has shown. [START_REF] Gragueb | Jarres et amphores de Ṣabra al-Manṣūriya[END_REF] Concerning jars and other kinds of ceramics, Sicily became a production area of jars exported full or even empty to serve as containers. Palermo jar sellers appear in Ibn Ḥawqal's treaty. 21 Exportation of ceramics from Sicily is mentioned in the Geniza documentation and confirmed by archaeological evidence found in excavations made in Ifrīqiya, especially in the area of Ṣabra al-Manṣūriya. [START_REF] Bramoullé | Le mobilier céramique dans la Méditerranée des X e -XII e siècles[END_REF] (p. 98) Map 6.1: Ifriqiya and Sicily during the Fatimid Era Some Sicilian jugs, usually used for olive oil, and jars of bigger size were bought empty by the Geniza traders who were often very concerned about the leakproof quality of these pieces. Even though the letters are not always easy to interpret, one can see that the quality of the jars produced in the island was not always as good as the traders hoped. 23 (p. 99) Strategic materials were also part of the island's exports. Shipbuilding was a major activity of the Fatimid Caliphate in which Sicily played a significant role. [START_REF] Bramoullé | La Sicile dans la Méditerranée fatimide (X e -XI e siècle)[END_REF] In the name of jihad, the Fatimids created one of the greatest navies of the medieval Mediterranean, victoriously raiding enemies from Alexandria to Almeria. 25 Sicily became a major source of supply for timber, pitch or iron. All medieval geographers refer to several logging sites around San Marco, Cefalú, and elsewhere. [START_REF] Ardizzone | Aḥsan al-taqāsīm fī ma'arifat al-aqālīm[END_REF] However, logging was not always easy at a time when the struggle against the Byzantines was raging. In the 960's, it seems that many of the Christian loggers who worked for the Fatimids around Demone fled to the nearest Byzantine strongholds of Taormina and Rametta. [START_REF] Dachraoui | Études d'orientalisme dédiées à la mémoire de Levi-Provençal[END_REF] The difficulty of finding new loggers was a source of concern for the caliph. "You will insist with him [i.e. the governor of the island, Aḥmad b. al-Kalbī] so that he may display the greatest zeal in this matter," wrote al-Mu'izz to his secretary Jawdhar (d. 973) after receiving a message from the governor mentioning problems with the loggers. [START_REF] Al-Amwāl | Sīrat ustādh Jawdhar. Inside the Immaculate Portal[END_REF] Lumber, pitch, but also iron from the mines of Sicily was exported to Mahdiya, the main arsenal of the dynasty. Ibn Ḥawqal writes that the iron mine near a place called Gharbiya was in the hands of the sovereign (sulṭān), and the iron was sent to the shipyard for the navy. 29 He emphasizes the high quality of the papyrus produced on the island. While a part of it was used to make the documents needed by the local government, the rest was braided to make the cables for ship anchors. 30 Commercial letters as well as al-Idrīsī report pitch (zift) and cade oil (qaṭrān) -a medicinal oil made out of juniper (Juniperus thurifera) and used to treat skin diseases. This was produced around Aci and (p. 100) exported through Mazara, as described in a lengthy letter written at this last port on the 7 th of September 1064. [START_REF] Al-Idrīsī | II: 596[END_REF] Several plants for textile crafts were also introduced to Sicily during the Fatimid period. The introduction of cotton thus seems to have occurred around the 10 th century. Plantations were found especially in the regions around Agrigento and Mazara. Reported as early as the Byzantine period, the culture of the silkworm mulberry tree also experienced a certain boom from the 10 th century. These plants allowed the development of quality textile crafts. The weaving of cotton and silk cloths is attested in Palermo, Syracuse, Demone, and in the region of Agrigento. The letters of the Geniza mention the many silks produced on the island. These were various pieces of fabric, as well as several types of dresses, blankets, scarves, and turbans.

The oriental gentleman had to wear a Sicilian silk turban for which he did not hesitate to spend twice as much as for the main garment 32 . Among the other famous productions were also very high-quality rugs or silk twill mattresses. The reputation of these goods spread far beyond Sicily and North Africa. Like almost all of the island's manufactured goods, they were, of course, sent to Ifrīqiya, but above all they were exported to Yemen and India. Their prices, between five and ten dinars each, made them luxury products that only the elite could afford. However, the less-privileged could nevertheless experience the softness and comfort of Sicilian products by purchasing second-class silk fabrics, the so-called lāsīn silk, exported en masse to Ifrīqiya and to Egypt. 33 Sicilian productions enjoyed a great reputation and their exports contributed to the increase in maritime traffic between Sicily and Ifrīqiya but also more widely throughout the rest of the Mediterranean.

THE GROWTH OF MARITIME TRADE IN SICILY

In spite of the relative silence concerning maritime traffic between Sicily and North Africa during the eighth and ninth centuries, it seems, nevertheless, that the military operations launched in Sicily by the Aghlabids did not substantively alter a dynamic that favored Mediterranean trade to an (p. 101) increasing degree. Recent scholarship has challenged Pirenne's assertion that the Muslim conquest of the southern shores represented a disruption to Mediterranean trade. Piracy is no longer seen as a sign of the disappearance of commercial traffic but evidence, rather, that commerce remained robust. 34 In fact, maritime trade can be attested from the 8 th century, when the Aghlabid dynasty (800-909) came to power in Ifrīqiya.

As it has been shown for the other territories subject to Muslim powers such as al-Andalus or 32 Shelomo D. Goitein, "Sicily and Southern Italy in the Cairo Geniza Documents," Società di Storia Patria per la Sicilia Orientale, 67 (1972) the principalities of the central and western Maghreb which had little by little implemented a sea policy, there is no reason to think the Aghlabids could not do the same. 35 The account of the conquest of Sicily by the emirs of Kairouan is a proof of the existence of at least one truce signed a little before 817 between the Aghlabids and the Patrice of Sicily. 36 If it was obviously a question of silencing the weapons, the text of the truce, as it is reported, stipulated that the Sicilian authorities not undertake to retain any of the Muslims who went to the island and wished to return home. In diplomatic terms, it was a good idea to let the Ifrīqiyan merchants go to Sicily to trade. We can assume that the reverse was true as suggested relations between these two territories before 827 likely. Such a situation, although poorly documented, was amplified when the Aghlabids took control of Sicily, particularly the ports of the western part of the island whose resources and wealth were well known to Muslims. 38 In another fatwa, composed at the end of the 9 th century, the jurist Yaḥyā b. 'Umar (d. 901) used an example referring to trade between Ifrīqiya and Sicily to explain how Islamic jurisprudence addressed nautical rental contracts. 39 This example also demonstrates how regular journeys between the two territories were (Maps 6.1 and 6.2).

After 910, the rise of Sicilian productions and the commercial traffic that passed through the island therefore owed nothing to chance. The local and, more broadly, the Mediterranean context was generally favorable to trade. From the 9 th century, the raids on Italian cities and the influx of gold from sub-Saharan Africa encouraged the monetization of the Sicilian economy and the minting of highly prized quarter dinars, 35 Christophe Picard, Sea of the Caliphs (Cambridge-London: The Belknap Press of Harvard University Press, 2018), 236-55. 36 Al-Mālikī, Riyāḍ, I: 270-1. Muhammad Talbi, L'émirat aglabide, 186-296/800-909 (Paris: Adrien-Maisonneuve, 1966), I : 402. Nef, " Comment," 195. 37 The Kalbid Emir Ja'far b. Yūsuf (r. 998-1019) was inspired by Fatimid Cairo to subdivide a district in his name, the Ja'fariya. 43 In Arabic and Judeo-Arabic literature, Palermo often appears as "the city" (al-madīna) or the "city of Sicily" (madīnat Ṣiqīliya) and simply Ṣiqīliya, a sign of its political and economic weight on the island 44 . There were many artisans and markets linked to court consumption. In the countryside, many farms belonged to the princes, and agricultural estates were in the hands of senior officials since, certainly, the tenth century.

In general, the Mediterranean context experienced a boom in maritime traffic increasingly controlled by the Italian cities interested in the profits they could derive from the resale of oriental products which arrived in large quantities in Egypt at first but were also shipped in mounting volume from Sicily when the northern Italian elites wanted to follow oriental fashion and sought a closer source than Alexandria. This vibrant commerce and the human network that flourished between Sicily, Ifrīqiya and Egypt is concretely reflected in numerous Geniza business letters. Nahray b. Nissīm, one of the most famous merchants in the Jewish community of Fusṭāṭ and recipient of Labrāṭ's letter in 1061, was himself concerned about the changing political conditions on the island. As many others, Nahray was native to Ifrīqiya where members of his family were still living. His own brother and uncle were active in Mazara and, like many Jewish (p. 104) merchants in Egypt, thanks to his network, he certainly did more business with Sicily and Ifrīqiya, a 13-50 days journey by sea, than with the ports of Palestine and Syria, about 5-7 days away by sea from Tinnīs, the main Egyptian port on the eastern branch of the Nil delta 45 . This is not to suggest that there was no trade between Egypt and Syria, but that the trade players were not exactly the same.

The Geniza letters testify to the central place that Sicily played in the Ifrīqiyan economy and, we can add, in the Egyptian as well. According to the Geniza letters, the messages written in Sicily and intended for Alexandria or Fusṭāṭ are more numerous than the letters written in 43 Alessandra Bagnera, "From a small town to a capital: The urban Evolution of Islamic Palermo," in A Companion to Medieval Palermo, ed. Annliese Nef (Leiden-Boston: Brill, 2013), 74-80. 44 Ibn Ḥawqal, Ṣūrat, 118. Kitāb gharā'ib al-funūn wa-mulaḥ al-'uyūn, ed. Yossef Rapoport, Emilie Savage-Smith (Leiden-Boston: Brill, 2014), fol. 34A, 130-131. TS-12. 270, fol. 1b, upper margin, l. 4. In Gil, Kingdom, IV: 483. 45 About Nahray family links see Jessica L. Goldberg, Trade and Institution inf the Medieval Mediterranean (Cambridge: Cambridge University Press), 33-45. For examples of length of such journeys see T-S 13 J 19, f. 20, fol. 1a, l. 8-9; T-8 J 20, f. 2, fol. 1b, l. 6; T-S 13 J 15, f. 9, fol.1a, ll. 9-10. In Gil, Kingdom, III: 30, 653, 815.

Ifrīqiya. 46 In 1047, Nāṣir-ī Khusraw, a Persian traveler in Egypt, confirms this. When he mentions Alexandria, he points out the commercial links between this port city and Sicily but is silent regarding trade with Ifrīqiya. 47 Sicily was the main base for the departure and arrival of commercial vessels that traded between Egypt and the Siculo-Tunisian space. The maritime traffic between Sicily and Ifrīqiya apparently consisted more either of a concentration of Ifrīqiyan products in Sicily, mostly olive oil, before export to Egypt or, on the contrary, of the redistribution of goods imported into the island. 48 However, the links between Sicily and Ifrīqiya were undoubtedly closer than what seems to emerge from the Geniza letters mentioning Sicily.

The close distance between the two areas makes this easy to understand. This link can be noted in several sources. Among them, are Islamic legal texts, mainly ship rental contracts from Ifrīqiya to Sicily or contracts between Ifrīqiyan traders willing to send or buy products to or from Sicily. Several fatwas from the end of the 10 th century and the beginning of the 11 th allude to juridical problems that occurred after the rental of ships between Sicily and the port of Sousse, north of Mahdiya, because storms (p. 105) deflected the ships from their initial destination. 49 These references to Sicily document regular traffic between the two territories.

Another very interesting document emphasizes this link: an anonymous map of Mahdiya which appears in the Kitāb gharā'ib al-funūn wa mulāḥ al-'uyūn, a book certainly made in Cairo sometime between 1020 and 1050.

This map shows the strong maritime ties between not only Mahdiya and Sicily but between the coasts of Ifrīqiya and those of Sicily. The drawing was clearly made to show the strength of the walls of the Fatimids's first capital, standing proudly on the Mediterranean shore 46 Annliese Nef, "La Sicile dans la documentation de la Geniza cairote (fin X e -XIII e siècle) : les réseaux attestés et leur nature", in Espaces et réseaux en Méditerranée, VI e -XVI e siècles, I, La configuration des réseaux, ed. Damien Coulon, Christophe Picard and Dominique Valérian (Paris: Bouchène, 2007), 276-83. 47 Nāṣir-ī Khusraw, Book of travels, ed. Wheeler M. Thackston (Costa Mesa: Mazda Publishers, 2001), 55. 48 T-S 10 J 20, f. 12, fol. 1a, ll. 14-15. In Gil, Kingdom, III: 640. 49 Al-Wansharīsī, Mi'yār, VIII : 310, 299-300.

against the enemies of Islam 50 . Technically and officially, when the map was drawn, Mahdiya was under Zirid control, and Sicily was the realm of the Kalbids rulers of Palermo. Both dynasties were representatives of the Fatimid sovereign in the central Mediterranean area, with the Emirate of Barqa in eastern Libya. [START_REF] Bramoullé | L'émirat de Barqa et les Fatimides : les enjeux de la navigation en Méditerranée centrale au XI e siècle[END_REF] The most original and interesting aspect of the image is the very clear link established between Mahdiya and Sicily, especially Palermo. In the notes that the author added just next to the drawing of Mahdiya's closed port, the administrative capital of Sicily is clearly referred to as Ṣiqiliya, which is usually the generic name of Sicily in Arabic. Under a note entitled "[list of] Ports (marāsī) from Mahdiya to Palermo (Ṣiqiliya)," he traces a maritime route which leads along the Ifrīqiya coast to Kalibia then, from this point, to Pantelleria, Mazara and, in a few more stages including Trapani, up to Palermo/Ṣiqiliya (Figure 1) 52 . After 1052, when the situation in Ifrīqiya worsened because of the arrival of the Arab Bedouins (the Banū Hilāl) sent by the Fatimids and while Sicily gradually came under Norman rule, the island remained a major supply center for North African cities and, more surprisingly, maybe, a more secure place for some Ifrīqiyan inhabitants as it appears in some fatwas and the Geniza letters like the one Barhūn b. Mūsā al-Tāhirtī wrote to Nahray after his settlement in Trapani, around 1053. 53 Reading these letters, it appears that even if the Jewish traders were sometime in shock or frightened because of the very dangerous situation (p. 106) they had to face, they almost never ceased their business. Among the conditions that provoked anxiety were the import taxes-regarded with almost as much apprehension as the report of the killings in Ifrīqiya.

Because it was not a general rule in the Fatimid area, when a tax or extra tax was required from the traders in Sicily, it was always underlined with great concern and even some exaggeration as we can note in a passage that refers to how people, because of the new tax, "preferred death to life." 54 In 1056, two letters to Nahray b. Nissīm report a tithe ('ushr), here referred as an import tax, suddenly demanded from merchants in Palermo. "Our friends in Sicily [i.e. Palermo seems to be meant here] have great misfortune since a tax was taken from the people of the city (ahl al-balad)" says the first one. 55 The second, written in Palermo on the 18 th of August is more precise, "I'm unable to sell anything at this moment since our friends here were asked to pay an extra import tax [….]…. This was the cause of the Sultan's demand for the tax. He heard rumours that people of the city were having partnerships with foreigners and disguising the goods as their own." 56 This measure was taken because the foreign merchants sought to avoid paying certain duties by making agreements with locals who paid lower import taxes, so the emir imposed a tithe on foreigners. It was experienced as a real injustice by the Geniza actors but, in fact, it concerned all foreigners and not only non-Sicilian Jewish merchants. This account testifies to the regularity of the presence of non-Sicilian merchants on the island. Because of this extra tithe, no profit was expected and, as a result, trade with Sicily came to a standstill. Maymūn, the author, clearly express his will to Nahray not to send anything to the island and urges that those he calls "their friends" or "their people", meaning their business partners, should leave for Mahdiya where the situation was more favourable even though it was a second-choice destination. Thus, we can assess the role of Sicily in trading activity. The island was clearly a stopover for anyone trading in the central Mediterranean. During the 11 th century, the prospect of finding in Sicily a certain number of local and oriental products encouraged people from al-Andalus and Italian cities such as Amalfi, Pisa, Naples and Venice to frequent the Sicilian (p. 107) ports. 57 The presence of so-called Rūm merchants is also attested by the Geniza letters. A letter written in Trapani about 1053 mentions the sale of pepper and perhaps also lacquer to the Rūm. 58 Another letter, written in Mazara in September 1064, confirms this information and provides some important details: "Last year I went to Palermo after the ships arrived. I got a bundle of pepper there, inside of which I found a bundle of very poor-quality black ginger. By God! No one here will take the value of a dirham from me, neither the Rūm nor anyone else [...] " and further on, the author specifies that in order to sell his ginger he had to resolve to enter into a partnership with a colleague who was going to "the land of the Rūm". 59 Ships generally left the Maghreb coasts loaded with the finest Ifrīqiyan products, mainly olive oil, bound for the ports of Sicily, according to a hierarchy which evolved over this period.

At first, the increasingly unstable Sicilian context did not penalize trade but, instead, favored a reorganization of the Sicilian port network. Ports like Trapani and especially Mazara strengthened their role to the detriment of Palermo. 60 With its "flax market" (sūq al-qattānīn), Mazara became the main port for ships sailing between Sicily, Ifrīqiya, and Egypt. Egyptian raw flax was exported in large quantities to the island where it was processed and re-exported to Ifrīqiya and all around the Mediterranean. Egyptian merchants anxiously watched for news of the flax's price in Mazara. This allowed them to adjust exports so as not to lower prices even 56 DK 230d, fol. 1a, l. 29, fol. 1b, ll. 3-4. In Gil, Kingdom, III: 858, 860. 57 Wilhelm Heyd, Histoire du commerce du Levant au Moyen-Âge (Leipzig: Otto Harrassowitz, 1885), I : 121-2. 58 ENA NS 18, f. 24, fol. 1b, l. 13. In Gil, Kingdom, III:130. 59 Dropsie College 389, fol. 1b, ll. 5-7. In Gil, Kingdom, IV: 466 60 Goldberg, Trade, 319 if demand was strong. In August 1063, a letter sent from Mahdiya to Fusṭāṭ cites several partners of both the writer of the letter, Mūsā b. Barhūn al-Tahertī, and the receiver in Fusṭāṭ.

It shows how information, documents and goods traveled easily between these places. More precisely Musa explains how he learned that an accounting document (ḥiΒāb) he was expecting from Egypt appeared to be in Sicily while he was thinking it was on its way directly from Alexandria to Mahdiya, and that one of his partners told him he would forward this bill to Mahdiya once he commuted to Sicily. Musa also informs his colleague in Egypt, Yeshu'a b.

Ismā'īl, about the level of flax prices (too low), and spices (too high), on the Mahdiyan and Sicilian markets, that were (p. 108) clearly linked, at this very precise moment, by the same economic conditions because both of them were dependent on the ships coming from Egypt with raw flax and spices. 61 As already noted, letters show not only that Egyptian flax arrived in Sicily and Mahdiya in huge quantities, but also oriental goods from the trade across the Indian Ocean. Pepper, cinnamon, ginger but also dyeing substances essential for textiles such as brazilwood, indigo, or even fragrant and pharmaceutical products like aloe wood, rose oil, myrobalan, lacquer, camphor were loaded in the holds of ships bound for Sicily and Ifrīqiya.

Hundreds of ships made the trips each season to and from Sicily, commuting from there to Ifrīqiya. For example, in two letters of 1053 and 1056 written in Alexandria, the authors allude to the same boats commuting between Sicily, Ifrīqiya, and Egypt. The letter of 1056 announces the arrival of ten ships from Sicily, each carrying 500 people 62 . There was nothing exceptional about such a convoy at the time. The names of the owners of the ships are all cited. Among them were some governors of Syro-Palestinian coastal towns; also mentioned was a boat simply called the "boat of the Sultan (markab al-sulṭān)", that is to say certainly, the ruler of Ifrīqiya at that time, al-Mu'izz b. Badis (r. 1016-1062) or maybe the Fatimid caliph al-Mustansir (r. 1036-1094). Both of them had boats active in the trade between Sicily, Ifrīqiya, Egypt and Syria. 63 The letter clearly shows that the island was in fact at the heart of a commercial network linking the entire Muslim world from al-Andalus to Syria and even well beyond.

CONCLUSION

Despite an increasingly troubled Sicilian context, Sicily's role as an alternative trade hub between East and West strengthened over the period between the ninth and eleventh centuries.

The ideal position of the island in the center of the Mediterranean, the development of a court concerned with consuming luxury products, as well as the privileged links with Cairo, favored 61 T-S 16.163, fol. 1a, l. 36, right margin, ll. 1-12, 13-15, fol. 1b, ll. 3, 6, 9, 20. In Gil, Kingdom, III: 249-52. 62 BM Or. 5542, f. 9, fol. 1a, l. 9; ENA 2727, f. 38, fol. 1a, ll. 4-5. In Gil, Kingdom, III: 629, 636. 63 Bramoullé, Les Fatimides et la mer, 670-5.

  by a fatwa from the first half of the 9 th century issued by the Sunni jurist Saḥnūn (d. 854) or his son (d. 869). It says it was illegal for Ifrīqiyan freebooters to raid Christian ships captured near Muslim ports or on the high seas and "known to trade with Muslims (miman 'urif bi-l-tijāra ilā' al-muslimīn)." 37 Evoking the law of war at sea and what it was possible to capture or not, the author thus indirectly highlights the regular presence of Christian ships near the Muslim ports of Ifrīqiya and the existence of maritime relations between Christian and Muslim shores of the Mediterranean. The proximity of Sicily to Ifrīqiya made the existence of commercial

  Saḥnūn quoted by al-Qayrawānī (d. 996), Al-Nawādir wa-al-ziyādāt 'alā al-Mudawwana min ghayrihā min alummahāt, ed. Muḥammad Ḥajjī (Beirut: Dār al-gharb al-islāmī,1999), III: 132. 38 Al-Istakhrī, Kitāb masālik al-mamālik, ed. Michael J. De Goeje (Leiden : Brill, 1927), 70. 39 Al-Wansharīsī, Mi'yār, VIII: 310-11.

Map 6 . 2 :

 62 The Fatimid Empire between the 10 th and the 12 th centuries. (p.103) which greatly facilitated trade 40 .Moreover, the cities of Sicily experienced notable growth. Palermo was gradually endowed with new districts. A " quarter of the Slavs" and even a "new quarter " made their appearance. 41 The map of Sicily in the Kitāb gharā'ib al-funūn wa mulāḥ al-'uyūn shows several of this quarters outside the walls of Palermo. 42 40 Michael Brett, "Ifriqiya as a Market for Saharan Trade from the Tenth to the Twelfth Century A.D.," The Journal Of African History 10, 3, 1969, 347-64. Samuel M. Stern, "Tari. The Quarter Dinar," Studi Medievali, 11 (1970), 177-207. 41 Ibn Ḥawqal, Ṣūrat, 119. 42 About the conception of the book and the maps in it cf. Yossef Rapoport, Emilie Savage-Smith, The Lost maps of the Caliphs (The University of Chicago Press: Chicago-London, 2018), 1-27.

  , 14.33 T-S 12.250, fol. 1a. l. 4; BM Or 5542, f. 22, fol. 1a, l. 6; AIU VII F 1, fol. 1a, l. 4, right margin, l. 5. In Gil, Kingdom, II: 447, 492, 827, 829.34 About this topic, see the preface by Christophe Picard to the new French reedition of Henri Pirenne's most famous book. Cf. Henri Pirenne, Mahomet et Charlemagne, rev. ed. (Paris: Presses Universitaires de France, 2005), v-xlv.

David Bramoullé, Les Fatimides et la mer (Leiden: Brill, 2019), 126-129.

Ibn Ḥawqal, Ṣūrat, 122.

local products as well as imports of the best products from Ifrīqiya and more broadly from all over the Muslim world. Trade between Ifrīqiya (p. 109) and Sicily flourished not only because of the historical relations but also because the island played a major role in the Fatimid economic and ideological strategy and because the pattern of Mediterranean trade between Egypt and the central Mediterranean privileged Sicily over Ifrīqiya once the Fatimids moved to Egypt. This context made the trip to Sicily more than worthwhile for some Italian merchants hoping to avoid the long and dangerous journey to Almeria, Alexandria or Tyre. The safe bet of obtaining there, almost as neighbors, goods in great demand in Europe undoubtedly compensated for the price or perhaps less choice and even the inferior quality of some of the goods compared to those that would have been possible to find in Egypt. The building of the Norman state did little to change Sicily's role, even if a growing number of Christians were likely to sail directly to Alexandria in the 12 th century.

Bibliography