Cosimo Lucci
email: cosimo.lucci@unifi.it

Niccolo Baldanzini

Pedro Huertas Leyva

Simone Piantini

Giovanni Savino

Thomas Lich

Jan Schumacher

Claire Naude

Adrien Canu

Christophe Perrin

Niccolò Baldanzini

Thierry Serre

Defining suitable parameters for safe and effective deployment of a motorcycle Pre-Crash Braking system: findings from field testing and crash simulations

ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Methods

First, a field test program involving 51 common riders as participants on two test vehicles was executed to assess the feasibility of different levels of autonomous braking intervention. The system was tested in the speed range of 30-50 km/h while performing typical manoeuvres including straight riding and lane change. Second, 60 crash cases sourced from two different in-depth databases from Italy and France were reconstructed using two different 2D simulation software, to test various obstacle detection system requirements and evaluate the potential safety benefits of the PCB intervention.

Results

In both straight-line and lane change manoeuvres, autonomous braking intervention reaching decelerations up to 5 m/s 2 with fade-in jerk up to 20 m/s 3 for a duration of approx. 1 s were considered manageable on both test vehicles by participants. Overall, the system intervention was tested more than 900 times with no loss of control. The crash simulation analysis indicated that a field of view of 80° and a detection range of 30m or higher can be adequate to effectively identify obstacles and trigger PCB. Tangible safety benefits were found to be achievable with several combinations of the analysed design parameters.

Introduction

This study presents the results of the collaborative research performed within the framework of the European Commission-founded project PIONEERS, whose general objective was to improve the safety of Powered-Two-Wheelers (PTWs) users through an innovative integrated approach to rider protection, based on personal protective equipment and onboard active safety systems.

Within the project, one of the cores of research was Pre-Crash Braking (PCB), being one of the most promising technologies among onboard safety systems in development for PTWs [START_REF] Terranova | Applicability Assessment of Active Safety Systems for otorcycles Using Population-Based Crash Data : Cross-Country Comparison among Australia , Italy , and USA[END_REF]. PCB provides the functionalities of Motorcycle Autonomous Emergency Braking (MAEB) in pre-crash conditions, delivering an autonomous braking action intended to reduce the pre-crash speed of the host PTW immediately before the crash. Such technology showed a positive effect on other road vehicles such as trucks and passenger cars [START_REF] Fildes | Effectiveness of low speed autonomous emergency braking in real-world rear-end crashes[END_REF].

The working parameters of PCB, intended as braking parameters, which define the performance of the precrash autonomous braking action, and obstacle detection requirements, which define the performance of obstacle detection tools required for effectively detect opponent vehicles or objects and trigger the PCB at the proper timing, are the key for safe and effective implementation of PCB on PTWs. As indicated in studies on passengers' cars, different parameters can provide different results in terms of impact speed reduction and injury mitigation [START_REF] V. Graci | Quantitative characterization of AEB pulses across the modern Traffic Inj[END_REF].

In order to explore suitable parameters for PCB intervention, early studies employed mainly two approaches: field tests to evaluate rider stability during the deployment of Automatic Braking (AB), and crash simulations to estimate PCB potential benefits for injury mitigation [START_REF] Savino | Active safety systems for powered two-wheelers: A systematic review[END_REF]. Studies focusing on field testing started in 2010 with professional riders and with a PTW equipped with a laser-scanner and producing automatic decelerations in correspondence with a target obstacle [START_REF] Giovannini | Analysis of the minimum swerving distance for the development of a motorcycle autonomous braking system[END_REF]. Further research was performed testing AB with common riders as participants and decelerations up to 2 m/s 2 deployed unexpectedly via remote control [START_REF] Savino | Exploratory field trial of motorcycle autonomous emergency braking (MAEB): Considerations on the acceptability of unexpected automatic decelerations[END_REF], and again, with professional riders in lane-change riding scenarios [START_REF] Merkel | imits of Autonomous Emergency Brake Systems for Powered Two-Wheelers -an Expert Study[END_REF]. Crash simulations were also employed to develop decision logic to trigger PCB interventions [START_REF] Savino | Triggering algorithm based on inevitable collision states for autonomous emergency braking (AEB) in motorcycle-to-car crashes[END_REF], and to explore its potential benefits on crashes [START_REF] Savino | A robust estimation of the effects of motorcycle autonomous emergency braking (MAEB) based on in-depth crashes in Australia[END_REF], [START_REF] Savino | Can Experienced iders Benefit from an Autonomous Emergency Braking System ?[END_REF].

In order to make PCB a mature technology to be introduced on standard vehicles, further research is required to define safe and reliable working parameters. Some preliminary studies which analysed its effectiveness, suggested that the parameters of intervention field-tested so far may not be sufficient to reduce the likelihood of sustaining serious injuries in case of crashes [START_REF] Piantini | Potential head injury mitigation of -AEB in real-world motorcycle crashes[END_REF]. In addition, the current technological development of obstacle recognition tools fostered by the introduction of Autonomous Emergency Braking for passenger cars and research for Autonomous Driving, offered in the last few years new reliable tools for obstacle detection, which could pave the way to an effective triggering of PCB.

The goal of this study is to identify suitable parameters of intervention and technical requirements for obstacle detection tools for a safe and effective application of PCB. We performed field tests with two prototype vehicles and participants to assess the acceptability of the PCB among end-users and the controllability of the vehicle with different sets of braking parameters, while computer simulations were used to evaluate PCB effects and its efficacy in reducing impact speed with a broader set of braking parameters and obstacle detection requirements.

Methods

This study combines two different methodologies -Field testing and Crash modelling-with the common goal of identifying suitable parameters for safe and effective deployment of Pre-Crash Braking system on Powered-Two-Wheelers (see Figure 1). In this section both the methodologies and the sets of PCB working parameters tested in field testing and simulations will be presented.

Field test methods

Field tests were performed on two different test vehicles provided with Automatic Braking (AB) devices capable of activating braking without rider action. Both vehicles (a sport-touring motorcycle and a two-front wheels scooter, from now on called Multistrada and MP3 respectively) were employed to test the intervention of AB in straight-line and lane-change manoeuvre.

The AB test procedure was developed based on previous studies based on pilot testing and literature review carried out by the authors [START_REF] Lucci | Investigating the feasibility of Motorcycle Autonomous Emergency Braking (MAEB): design criteria for new experiments to field test automatic braking[END_REF]. The AB interventions were tested at different velocities ranging from 30 km/h to 60 km/h (depending on the requested manoeuvres).

The participants were recruited among active riders with two years or 10000 km of riding experience and aged between 20 and 65. The advertisement for the participants' recruitment was disseminated through the university web page, social media, flyers and biker groups.

This study obtained ethical approval from the Ethics Committee of the University of Florence (Written opinion N. 46, 20/03/2019).

Test procedure and AB parameters

Participants tested the intervention of the AB system by riding with one of the two test vehicles along the test track: the AB activations were manually triggered by one investigator via remote control [START_REF] Lucci | emote controlled braking actuation for motorcycle safety system development[END_REF]. The AB was triggered only when the PTW was in precise spots of the track while the participants were performing the specific manoeuvres.

For the Multistrada, the test included two phases with a nominal deceleration of respectively 3 m/s 2 and 5 m/s 2 and fade-in jerk of 15 m/s 3 tested in four manoeuvres (straight-line, lane-change, slalom, and curve). For the MP3, as for the Multistrada, the test included two phases with a nominal deceleration of respectively 3 m/s 2 and 5 m/s 2 and fade-in jerk of 15 m/s 3 , tested in two manoeuvres (straight-line and lane-change). The test with MP3, after the above-mentioned phases, also included two other phases with fade-in jerk up to 25 m/s 3 . The participants were not aware of the timing of AB intervention nor the exact position within the test track: this aimed to obtain AB events that were as unexpected for the rider as possible while keeping a low learning effect. Overall, the AB was deployed in the different manoeuvres with an average frequency of one activation every 100 s of riding and with a pseudo-random order. Full details of the test procedure were presented in [START_REF] Lucci | Autonomous Emergency Braking system for Powered-Two-Wheelers: testing end-user acceptability of unexpected automated braking events deployed pre-crash trajectories[END_REF].

Test vehicles

The first test vehicle was a Ducati Multistrada 1260S, a sport-touring motorcycle equipped with Motorcycle Stability Control (MSC), combined braking and semi-active suspensions. The vehicle was provided with outriggers to prevent the vehicle from lateral fall (see Figure 2 -left), since the intervention of AB in lateral manoeuvres such as cornering and slalom was also tested with this vehicle, but it will not be presented in this paper. The second vehicle was a Piaggio MP3 500, a two-front-wheel scooter provided with Antilock Braking System (ABS) (see Figure 2

Data recording

A similar data acquisition system was employed on both vehicles to collect data from the PTWs' CAN-Bus (throttle, brake action, steering angle, vehicle tri-axis acceleration and gyro), from an Inertial Measurement Unit (IMU) attached to the back of the participants to record the chest movement during the tests, and from an internal tri-axes accelerometer and GPS receiver. Both test vehicles were also equipped with action cameras to record the driver's body and monitor his/her behaviour during the AB. In order to collect subjective data, questionnaires were adopted to ask participants their opinion on the test, the AB system tested and the controllability of the vehicle during the AB activation in the different manoeuvres.

Crash simulation methods

The second step of this study employed computer simulations to reconstruct real-world crashes and assess the potential benefits of PCB applied with different parameters of intervention. The simulations were designed to cover a broad range of PCB parameters, including those tested in the field test campaign. Also, different levels of performance for the obstacle recognition tools supposed to trigger PCB were analysed.

Crash data source

Crash cases for simulation were extracted from two different in-depth road crash databases: the InSAFE database from the University of Florence (UNIFI), which collects crashes from the Florence metropolitan area, Italy [START_REF] Piantini | Advanced accident research system based on a medical and engineering data in the metropolitan area of Florence[END_REF], and the EDA database from the University Gustave Eiffel (UGE), which collects crashes from both rural and urban roads in France [START_REF] Canu | Interest of in-depth investigation for studying the relation between speed and accident risk[END_REF]. In total sixty cases were employed, thirty from each database, extracted and reconstructed based on the detailed description of the crash collected in the database, including for example road configuration, marks documented in the crash scenario, damage to vehicles, injuries of riders, and police reports. Overall, crashes included in the study involved mainly L3 PTWs (77%) and 23% of L1 PTWs only. They occurred mainly at intersections (70%), while only 22% were in straight-line and 8% in curves. The distribution of the crash configuration among the two databases was slightly different: the InSAFE dataset collected more Head-to-side (T-bone) crashes (56%), while in the EDA database 50% of cases were Head-on crashes (see Table 1 -for the detailed definition of the crash configurations see [START_REF] Piantini | Assessment of the effect of otorcycle Autonomous Emergency Braking (MAEB) based on real-world crashes[END_REF]). A lower proportion of Head-to-rear and Sideswipe crashes were included in both databases.

Crash reconstruction tools

Crash reconstructions were performed on two different 2D simulation tools developed by UNIFI and UGE based on previous studies on PCB [START_REF] Savino | A robust estimation of the effects of motorcycle autonomous emergency braking (MAEB) based on in-depth crashes in Australia[END_REF]. Among the 60 cases included in the study, 20 were simulated in both crash simulation tools (10 from each database), to compare results from the two different software. Each crash case was first reconstructed in the virtual environment and validated using all the information collected in the database (e.g., comparing the impact speed at the crash and the incidence of the two vehicles involved in simulations with detailed data from crash investigators). Then, the intervention of PCB with different parameters was simulated (see the following section). The effect of PCB was measured in terms of Impact Speed Reduction (ISR), as the difference between the impact speed without and with PCB.

PCB tested parameters

Crash simulations were employed to assess the influence on PCB effectiveness of five parameters, three related to the automatic braking system (Triggering Strategy, Deceleration and Fade-in Jerk), and two related to the obstacle recognition system (Field of View and Range). See Table 2 for full details about the ranges and the incremental steps used for simulations.

The Triggering Strategy defines the timing of deploying PCB based on the detection of the inevitable collision state: the time in which the crash between the PTW and the opponent vehicle/object becomes unavoidable.

Based on different thresholds of deceleration in longitudinal and lateral directions achievable by the PTW, it is possible to define different triggering strategies. These correspond to a different time to collision at which the PCB is triggered. Full details of the definition of triggering strategies are presented in [START_REF] Savino | Inevitable Collision States for otorcycle-to-Car Collision Scenarios[END_REF]. For this study, three triggering strategies (called "Conservative", "Standard" and "Progressive") were simulated in both crash simulation software. In order to have a more realistic PCB behaviour, the software employed by UGE added to PCB simulation a constraint on times to collision with the realistic values of 0.6 s (Conservative), 0.8 s (Standard) and 1 s (Progressive).

Three values of PCB Deceleration were employed in crash simulations: two of these values (respectively, 3 m/s² and 5 m/s²) were devised by field tests performed with participants (see section 2.1.1), while the highest value of deceleration (7 m/s²) was tested to assess what could be the potential benefits of PCB with decelerations even higher than those currently field-tested with participants. Similarly to deceleration, the two levels of Fade-in Jerk tested with participants were also employed in simulations.

The Field of View represents half of the width in degrees of the detection zone of the obstacle recognition system. Combining its value with the Range, we can define the obstacle recognition cone in which an opponent vehicle or object can be recognised by the system (see Figure 3). This defines the timing when the other vehicle is detected by embedded sensors on the PTW and therefore PCB can be triggered. The Range is the maximum distance at which the PCB can detect an opponent vehicle/object. For both parameters, a wide range of values was tested in simulations, based on the state-of-the-art radar technology. It is evident that state-of-the-art sensor devices are capable to have a wider range. However, to limit simulation time, for PCB with progressive triggering strategy the range does not extend 90 m. The wide number of parameters tested allowed us to assess the influence of each parameter on PCB performance (see section 3.2.1). However, 450 different combinations of PCB parameters tested did not allow us to obtain a realistic assessment of the expected benefits provided by the system. Three combinations of parameters were therefore selected to analyse the potential effectiveness of PCB considering a pessimistic (low efficiency), an average, and an optimistic (high efficiency) implementation of parameters. The sets of parameters selected for the three configurations are displayed in Table 3.

Based on results from field testing (see section 3.1.4), for the PCB deceleration, the more conservative setting (3 m/s²) was selected for the pessimistic configuration while for the average and progressive configurations the deceleration of 5 m/s² was chosen. Similarly, the fade-in jerk was set to 15 m/s 3 for the pessimistic configuration and 25 m/s 3 for both the average and optimistic configurations. Deceleration (m/s²)

3 5 5
Fade-in jerk (m/s 3 ) 15 [START_REF] Ucci | otorcycle Autonomous Emergency Braking (MAEB) employed as enhanced braking: estimating the potential for injury reduction using real-world crash modeling[END_REF] 25

Range (m) 30 30 30

Field of View (°)

+/-15 +/-45 +/-45 3 Results

Field test results

The results of the field-testing activity will be presented in this section: actual PCB working parameters fieldtested for both test vehicles will be related to their feasibility in different riding conditions and acceptability among users.

Test participants

Overall, 51 participants (10 women, 41 men) were included in this study, testing only one of the two vehicles. Thirty-one participants tested AB on the Multistrada, while 20 on the MP3. Participants were selected based on their main usage of PTWs: the majority of participants who tested AB on Multistrada were mainly leisure riders while participants selected to test the AB intervention on the MP3 were mostly commuters. The age of participants ranged from 21 to 59 years, and they were characterized by different levels of education and a broad range of riding experience. For further details on the sample of participants included in the study please see [START_REF] Lucci | Autonomous Emergency Braking system for Powered-Two-Wheelers: testing end-user acceptability of unexpected automated braking events deployed pre-crash trajectories[END_REF].

Tested Automatic Braking intervention and manoeuvres

Table 4 reports a summary of the AB-tested intervention for the two test vehicles in the two manoeuvres considered in this study: straight-line riding and lane change reproducing an avoidance action (see Figure 4). Due to weather conditions, not all the participants were involved in testing the AB in all the manoeuvres and with all the levels of intervention planned in the test protocol.

Overall, the AB was tested with the Multistrada almost 250 times in straight line and lane change, whereas considering also the trials in different conditions and manoeuvres more than 500 AB tested interventions were recorded. With the MP3 the AB intervention was tested approx. 290 times the same manoeuvres.

For the Multistrada, the AB was deployed at two different levels of nominal deceleration (respectively 3 m/s 2 and 5 m/s 2 ), and with a fade-in jerk level of 15 m/s 3 . These nominal values were also measured after testing. Similarly, for the MP3 the two values of deceleration (3 m/s 2 and 5 m/s 2 ) were measured in the trials, while the two levels of fade-in jerk (respectively 15 m/s 3 and 25 m/s 3 ) set for the test resulted in a wide distribution of values of fade-in jerk, with peaks reaching up to 30 m/s 3 .

The AB duration for both vehicles was approx. 1 s (respectively, 1.08 s and 0.97 s for Multistrada and MP3), while the riding speed at AB trigger ranged from 37 to 45 km/h.

PCB intervention during avoidance action

Being the feasibility of PCB intervention when the rider is performing lateral maneuvers one of the main open issues when assessing its safety and applicability, an in-depth analysis of PCB intervention during lane-change maneuver reproducing avoidance action was performed [START_REF] Ucci | Field testing the applicability of motorcycle autonomous emergency braking (MAEB) during pre-crash avoidance manoeuvre[END_REF].

Vehicle dynamics in the lane change manoeuvre with and without automatic braking were compared (see Figure 5): minor effects were found on vehicle dynamics -except for those produced by the automatic brakingwhich never questioned the controllability of the vehicle. For both vehicles, participants were always able to manoeuvre the lane change by avoiding the virtual obstacle without executing other actions or braking. Due to the automatic deceleration and lower speed, minor differences in the vehicle lean were reported. No loss of control was reported by the participants in the questionnaire nor recorded by cameras.

Users' acceptability of 5 m/s 2 PCB deceleration

At the end of the test, the participants assessed the Automatic Braking system based on the conditions they experimented. Even if after testing the AB there were few negative opinions about it, for both test vehicles all the participants managed to complete the whole test without asking to interrupt the trials due to the intervention of the AB or other reasons. Moreover, no potentially dangerous situations were created by the intervention of the AB or the participants' behaviour.

The perception of the intensity of AB intervention in terms of braking deceleration and fade-in jerk is displayed in Figure 6 for both test vehicles.

Crash simulation results

The results of the crash simulation activity will be presented in this section: first, the influence of different PCB working parameters on Impact speed Reduction will be presented, second, the effect of three different sets of PCB parameters (an optimistic, average, and pessimistic configuration) will be compared.

Influence of PCB parameters

A total of 60 crash cases (half from the InSafe database and half from the EDA database) were employed to assess the influence of PCB working parameters such as triggering timing, braking deceleration and the fadein jerk. The same set of 60 cases was also used to simulate the effect of obstacle recognition parameters such as Field of View (FOV) and Range.

In order to assess the influence of each parameter, simulations were performed employing a standard set of parameters (Standard triggering, Deceleration = 5 m/s 2 , Fade-in jerk = 25 m/s 3 , Field of View = 40°, and Range = 30 m), and by varying only one parameter at a time.

Triggering

Setting all the other parameters to the standard value and varying only the triggering strategy, median reductions in impact speed of 5 km/h (conservative), 7.5 km/h (standard) and 12 km/h (progressive) were obtained (see Figure 7).

Deceleration

The PCB deceleration turn out to provide the highest influence on impact speed reduction: comparing ISR produced by 3, 5 and 7 m/s² PCB deceleration, the median speed reduction obtained by PCB intervention was, respectively, 2.5 km/h, 7.5 km/h and 9 km/h, using the standard setting for the other parameters (see Figure 8).

Fade-in jerk

Regarding the fade-in jerk, its influence on ISR among the two levels tested in the simulations was found to be limited (about 1 km/h) among the 60 cases (Figure 9). A median impact speed reduction of 6 km/h was estimated for a Fade-in jerk of 15 m/s 3 using standard values for all the other parameters, while 7 km/h ISR was obtained for a Fade-in jerk of 25 m/s 3 .

Field of View

Figure 10 shows the influence of the Field of View employing the standard set of parameters. With a FOV of 10° (on either side of the longitudinal axis of the PTW, i.e., 20° of total aperture), the detection was zero in at least half the cases. At 25° FOV, the median impact speed reduction was 4 km/h, at 40° it was 7.5 km/h while beyond 40° the ISR gain was very limited.

Range

Due to limitations in the simulation tools, the influence of the Range on ISR was analyzed by employing only 40 cases simulated by Univ. Eiffel: 30 cases from EDA and 10 from InSafe. The influence of the Range was however very limited: using the standard set of parameters, only a small difference between a range of 30 m and a range of 45 m was found (ISR increase of 0.2 km/h), while beyond 45 no increase of ISR was measured. Also using a different set of parameters (defined as "optimistic" -see section 2.2.3), the difference between the Range of 30 m and 40 m was limited (an increase of the average ISR of 0.4 km/h).

Realistic PCB configurations

From the large number of parameters considered in this study for the analysis of PCB effects, three realistic combinations of parameters were selected to represent typical system effects assuming a pessimistic (low efficiency), average, and optimistic approach (high efficiency). Considering all 60 simulated crashes in the three configurations, median reductions in impact speeds of 0.0 km/h, 7.4 km/h and 11.6 km/h were obtained (see Figure 11 -left). In 15 crash cases, the PCB was not triggered with any of the three configurations, or its intervention did not produce any effect (e.g., in cases in which the opposing vehicle was not detected in time, or the rider is manually braking with a higher deceleration than that produced by PCB). Excluding these cases, and therefore selecting crashes in which PCB is applied effectively, the median ISR was, respectively, 2.8 km/h, 10.7 km/h and 15.1 km/h for the three PCB parameter configurations (see Figure 11 -right). In 8 crash cases, at least one of the three configurations prevented the crash. The identification of suitable working parameters is the key to the future introduction of Pre-Crash Braking (PCB) on standard Powered-Two-Wheelers (PTWs). This study, results of the EC-founded PIONEERS project, merged two different approaches, field testing in the real world with common users as participants and crash simulations, to identify a set of appropriate parameters which can make PCB safe and effective in reducing injuries to PTW users.

The field tests campaign, which involved 51 participants and two different test vehicles, aimed to assess the feasibility and acceptability of PCB in the real world for a broad range of working conditions and parameters, which were never been tried before [START_REF] Marra | The future of the Autonomous Emergency Braking for Powered-Two-Wheelers: field testing end-users' acceptability in realistic riding manoeuvres[END_REF]. The sample size of participants employed for field testing was the widest so far in the field research concerning autonomous braking (PCB and MAEB). The system intervention was tested more than 1000 times on the two different types of vehicles with different parameters and manoeuvres. All the participants completed the experiment and agreed to test the intervention of the AB unexpectedly in the conditions proposed by the investigators and no dangerous situation occurred in the context of the deployment of AB. The sample of participants was characterized by a wide range of ages, sex, riding experience and motivations for riding. However, despite this large sample and the wide variability, the participants involved in this study may not be completely representative of all PTW user populations. They expressed generally a positive opinion about the system tested in both test vehicles, as the controllability of the PTWs was never at risk. Participants were always able to execute the avoidance manoeuvres, even with the highest level of PCB deceleration. The subjective assessment [START_REF] Ucci | The acceptance of Autonomous Emergency Braking System for Motorcycle: results before and after testing[END_REF] and objective data analysis performed based on these tests [START_REF] Ucci | Field testing the applicability of motorcycle autonomous emergency braking (MAEB) during pre-crash avoidance manoeuvre[END_REF]- [START_REF] Ucci | The acceptance of Autonomous Emergency Braking System for Motorcycle: results before and after testing[END_REF], [START_REF] Cassese | Analysis of the rider's body movement during the intervention of the Autonomous Emergency Braking system for otorcycles ( AEB)[END_REF] indicated the applicability and feasibility of PCB with 3 m/s 2 and 5 m/s 2 of deceleration and up to 20 m/s 3 of fade-in jerk, for interventions of up to 1 s duration.

The computer simulation approach was applied to sixty real-world crashes sourced from the InSafe and EDA databases, which were employed to estimate the effects of PCB and explore the influence of different sets of working parameters on its efficacy. Using two different simulation tools developed by the University of Florence and the University Gustave Eiffel, crashes were kinematically reconstructed and the PTW impact speed reduction provided by PCB was used as a reference for its efficacy, being strictly related to injury reduction [START_REF] Ding | otorcyclist injury risk as a function of reallife crash speed and other contributing factors[END_REF]. A large number of parameters were considered in the analysis concerning the autonomous braking performance (deceleration, fade-in jerk, and triggering) and obstacle recognition tools performance (field of view and range). This allowed for a comprehensive assessment of the influence of each parameter on impact speed and the identification of three realistic combinations of PCB system settings. Deceleration and triggering were found to be the most important parameters to maximize the effects of PCB, while a Field of View of the obstacle detection system equal to or higher than 45° (so overall 90° of view) was found not to be beneficial to increase PCB capabilities to detect obstacles. The three realistic sets of parameters representing respectively, pessimistic, average and optimistic conditions for PCB parameters provided median impact speeds reductions of, respectively, 0 km/h, 7.4 km/h and 11.6 km/h. These values, which are affected by different riding conditions and manual braking actions of the rider, are in line with studies focusing on different traffic environments and are potentially capable to mitigate injuries and fatalities [START_REF] Ucci | otorcycle Autonomous Emergency Braking (MAEB) employed as enhanced braking: estimating the potential for injury reduction using real-world crash modeling[END_REF].

This study identified the influence of the key working parameters of Pre-Crash Braking, one of the most promising technologies to enhance the safety of PTW users, on its effectiveness in terms of braking action and obstacle recognition. These results can be employed by manufacturers and researchers to tune the braking intervention, design the detection system and develop the triggering algorithms and therefore further develop Autonomous Braking for PTWs, towards its introduction on standard vehicles. Also, the combined approach of field-testing computer simulation developed for this study can be a reference for future studies aiming at the development of new active safety systems for PTWs.

Figure 1 -

 1 Figure 1 -Methodological approach employed for this study

  -right).

Figure 2 -

 2 Figure 2 -Test vehicles: Ducati Multistrada 1260 (left) and Piaggio MP3 500 (right)

Figure 3 -

 3 Figure 3 -Crash simulation tools employed for the study by UNIFI (left) and UGE (right)

Figure 4 -

 4 Figure 4 -AB activation in the two manoeuvres: 1) Multistrada in straight-line, 2) Multistrada in lane-change, 3) MP3 in straight-line, and 4) MP3 in lane-change.

Figure 5 -

 5 Figure 5 -Comparison of acceleration (blue) and vehicle lean (green) between a lane change with (solid) and without (dotted) AB. Left -3 m/s 2 AB intervention on Multistrada; Right -5 m/s 2 AB intervention on MP3

Figure 6 -

 6 Figure 6 -Perception of AB intervention for Multistrada (left) and MP3 Scooter (right)

Figure 7 -

 7 Figure 7 -Influence of the Triggering in PCB simulation Figure 8 -Influence of the Deceleration in PCB simulation

Figure 9 -Figure 10 -

 910 Figure 9 -Influence of the Fade-In Jerk in PCB

Figure 11 -

 11 Figure 11 -Impact speed reductions for the three realistic PCB configurations considered (Left: all 60 cases -Right: 45 cases with PCB really triggered)

Table 1 -

 1 Crash Configuration distribution of 60 cases among the two databases

	Crash Configuration	InSAFE	EDA	Total
	Head-on
		5 (16.7%)	15 (50.0%)	20 (33.3%)
	Head-to-rear
		3 (10.0%)	2 (6.7%)	5 (8.3%)
	Head-to-side
		17 (56.7%)	7 (23.3%)	24 (40.0%)

Sideswipe 5 (16.7%) 6 (20.0%) 11 (18.3%) Total 30 (100.0%) 30 (100.0%) 60 (100.0%)

Table 2 -

 2 PCB Parameters variation

	Parameter	Range	Incremental step
	Triggering strategy	[conservative, standard, progressive]	-
	Deceleration	[3 m/s² -7 m/s²]	2 m/s²
	Fade-in Jerk	[15 m/s 3 -25 m/s 3 ]	-
	Field 0f View	+/-[10°-70°]	15°
	Range	[30 m -90 m]	15 m

* NOTE: this value represents half of the whole FOV of the detection cone

Table 3 -

 3 Sets of parameters for the three PCB realistic configurations

	Parameter	Pessimistic	Average	Optimistic
	Triggering strategy	Conservative	Standard	Progressive

Table 4 -

 4 Summary of AB tested interventions

	Test Vehicle	Participa nts	Manoeuvre	Nominal decelera tion [m/s 2 ]	N° of PCB activation s	Initial Speed [km/h] Mean SD Mean SD Mean SD Mean SD Event Deceleration Fade-in jerk duration [s] [m/s 2 ] [m/s 3 ]
			Straight-line	3	63	47.6 4.7 1.07 0.03 2.9 0.3 15.
	Ducati Multistrada	31

Acknowledgement

The authors would like to acknowledge Ducati Motor Holding SPA and Piaggio & C. SPA for their support in this project.

Funding

This paper is part of a project that has received funding from the European Union's Horizon 2020 research and innovation program under Grant Agreement N° 769054, project PIONEERS (Protective Innovations Of New Equipment for Enhanced Rider Safety).

Disclosure statement: All authors have read and agreed to the submitted version of the manuscript. The authors declare no conflict of interest.


Dr Pauline Piraud-Fournet

Pierre-Marie Blanc

Thibaud Fournet

Khalifah Al-Rowaili

Saud Al-Tamemi

Tara Steimer-Herbet

The 2021 Season of the Upper Wâdî as-Sirhân Survey Project *

May

 -Pl. 1), are supposed to still preserve remains dated to the Nabataean, Roman and Byzantine periods.

As specialists of these latter Periods and ancient basalt construction, one of the aims of P.-M. Blanc, T. Fournet and P. Piraud-Fournet was also to reassess and document monuments and sites that can provide information regarding the occupation of the possible northeastern margins of the Nabataean kingdom and Roman and Byzantine Empire, through an inventory and a proper mapping of their possible architectural remains.

Introduction

This report presents the main results of the exploration survey undertaken in the northern part of al-Jawf Province between September 25 th and October 5 th 2021. The survey followed the meeting organized in 2019 in Riyadh between A. Zahrani (Saudi MoC), H. Rozier (French Embassy) and P. Piraud-Fournet (European Commission -Paris 1 Sorbonne). Its objective was on the one hand to start the architectural survey, description and study of the main ancient buildings previously identified in the Upper Wâdî as-Sirhân, also referred as the Qurayyât al-Milh ("Salt villages") area. On the other hand, it aimed to contribute to the assessment of the amount, quality and perhaps touristic values of archaeological resources and heritage in this area. In fall 2021, on the field, the team was composed by Dr Pauline Piraud-Fournet, Pierre-Marie Blanc & Thibaud Fournet (CNRS), Khalifah al-Rowaili, Saud al-Tamemi & Jaza al-Harbi (MoC); the survey was funded by the Saudi Ministry of Culture, French Embassy, European Commission HOLYHOST Research Programme and University Paris 1 Panthéon-Sorbonne, ArScAn UMR 7041-CNRS and we want to warmly thank the institutions and people who made this survey possible.

The report first reminds the historical importance of the region of the Upper Wâdî as-Sirhân and the previous surveys and studies carried out. In a second part, it provides a description and first analysis of the sites recorded during the mission.

The geography of the Wâdî as-Sirhân (the "Valley of the wolf") is featured by a shallow depression running over 500 km in a southeasterly direction from Bosra-Bostra (Southern Syria) to al-Jawf (Northern Arabia) on the fringes of the Nafud desert [START_REF] Winnett | Ancient Records from North Arabia[END_REF]Reed, 1970: 56 and[START_REF] Wasse | The Wâdî as-Sirhân Project: Report on the 2002 Archaeological Reconnaissance of Wadi Hudruj and Jabal Thawra, Jordan[END_REF][START_REF] Wasse | The Wâdî as-Sirhân Project: Report on the 2002 Archaeological Reconnaissance of Wadi Hudruj and Jabal Thawra, Jordan[END_REF] 1-2) (Fig. 1 -Pl. 1). The eastern margin of the Wâdî as-Sirhân is clearly defined by the western edge of the basalt desert (Harra), itself an extension of the volcanic uplands of the Jebel al-'Arab in southern Syria. The flint and gravel plains of eastern Jordan drop gently down to it through a series of tributary wadis running from south-west to north-east. Permanent water sources are now restricted to a small number of oases (Kâf and Ithrâ for instance) located on the eastern side of the wadi along the edge of the basalt. However, there is documentary evidence to suggest that marshes and wetlands survived in the basin from the Lower and Middle Paleolithic until well into the Mediaeval period. Throughout history, the Wâdî as-Sirhân has been considered as one of the principal routes from the southern Levant into the Arabian Peninsula. Furthermore, good agricultural conditions are found in two locations which form a group of oases-villages. The first one formed the Qurayyât al-Milh located not far from the Jordan-Saudi Arabian border, the second group is found in the Jawf region further south. As early as the middle of the nineteenth century, scholars have taken interest for the history and the heritage of Northern Arabia, even if only a few archaeologists ventured further east into the Wâdî as-Sirhân, which is located away from the medieval and modern pilgrimage routes. Yet, as historians such as N. Glueck in the 1940s, and more recently D. [START_REF] Graf | The Saracens and the Defense of the Arabian Frontier[END_REF]1989), G. [START_REF] Bowersock | Roman Arabia[END_REF] and T. [START_REF] Bauzou | La Praetensio de Bostra à Dumata (El-Jowf)[END_REF] reminded it, the Wâdî as-Sirhân is a key place in the history of the Near East because of its location between the Arabian Peninsula, Syria and Mesopotamia. It can be assumed to have been an attractive location for human occupation from the Lower and Middle Paleolithic, and in the Early Bronze Age. The presence of a number of wells located along the wadi indeed made it the favorite route for caravans travelling between Syria and North Arabia (Winnett and Reed, 1970: 56.). Before the Roman period, security and control of the road through the Wâdî as-Sirhân would have been placed under the responsibility of Nabataean desert patrols (Bowersock, 1983: 155). After AD 106, the Roman army took it over and was based in the cities of the Decapolis, in Bostra, capital city of the Provincia Arabia and in the oases of Dûmat al-Jandal, modern al-Jawf. Thus, the settlements on the northern side of the Wâdî as-Sirhân were probably

Previous Studies, Surveys and Identified Remains

So far, a few field surveys were undertaken in the area to identify sites, document ancient monuments, collect samples of pottery in order to date the occupation of the sites, search for ancient inscriptions. Following the work of previous explorers in the nineteenth and twentieth centuries, such as J. [START_REF] Euting | Tagebuch der Reise nach Syrien[END_REF] who provided picturesque drawings of Kâf and Ithrâ villages (Fig. 3 -Pl. 2), the most relevant archaeological survey in the northern Wâdî as-Sirhân took place in 1962. It consisted on a three day-survey undertaken by F.V. Wennett and W.L. Reed (1970) who highlighted important remains in Kâf and Ithrâ areas. According to them, these remains include, in Kâf, an imposing citadel called Qasr as-Sa'îdî and an hypothetical Nabataean temple transformed into a mosque within the citadel; in Ithrâ, an ancient Qasr north to the oasis, and a hypothetical Nabataean temple in the southeastern district of the oasis-village called Râslaniyah. South to the village, they also recorded a stone bearing a Nabataean inscription, found near a small room "now almost buried in the sand" (Winnett and Reed, 1970: 56-64). In the northern city of al-Hadîthah, they identified the remains of an ancient irrigation channel possibly dated to the medieval Arab period and the ruins of a qasr and ancient cemetery with graves and sherds of the Late Byzantine or Early Arab period. Near Qarqar, they visited the Umm Ayash massif. In all the region, they recorded Thamudic, Nabataean and Safaitic (and one Palmyrenian) inscriptions.

In 1976, an exploration of the Northern Wâdî as-Sirhân was included in the Saudi Arabian Comprehensive Archaeological Survey Program launched by a team of Saudi and foreign specialists. They published a preliminary report of the first phase to present the initial findings [START_REF] Mcc | Saudi Arabian Archaeological Reconnaissance 1976. Preliminary Report on the First Phase of the Comprehensive Archaeological Survey Program[END_REF]. P.J. Parr carried out the 1976 expedition in Kâf and Ithrâ areas, that recorded about thirty sites or monuments. According to Parr, the occupation of the Wâdî as-Sirhân in ancient times mainly consisted of villages and burial grounds belonging to Transjordanian peoples and the major occupation of the area could be dated, by comparison with pottery provided by well-studied Jordanian sites, approximately to the 7 th century Iron Age II (Parr 1989: 44-48).

In 1996, a one day-survey done by [START_REF] Al-Muaikil | Al-ʾāṯārwa-l-kitābāt al-nabaṭiyya fī minṭaqat al-jawf[END_REF] identified and added to this list some characteristic Nabataean period pottery as well as Iron Age pottery and graves (rukamiyya) to the north and east sides of the Kâf oasis.

In 2000, a team in charge of the registration and documentation of the Kâf Archaeological Palace published an important volume [START_REF] Al-Hussaini | Documentation & Registration of Kâf Palace in Qurayyât[END_REF]. Since this volume has not been distributed outside the Qurayyât region, we only learned of its existence when we arrived in Kâf, thanks to Khalifah AL-Rowaili. The group of authors, Saudi architects and archaeologists, recorded and dated new archaeological sites, such as, in Kâf, Qasr A'qelat al-Masha'an recently unearthed, dated to the Iron Age and, in Ithrâ, Qasr al-Kharab, located on the southern side of the road, at the foot of Jebel Radwa and possibly dated to the Iron Age.

In 2018, we asked Dr Tara Steimer, who is a specialist of Bronze Age settlements in Southern and Basaltic Syria, to have a look of the area through Google Map's Satellite images (Annex Document -last page). She identified a large amount of remains belonging to pre-classical periods, such as tombs, enclosure, dwellings, Desert Kites and so on, which are the type of structures that Parr and his colleagues started to document in the field in 1976 [START_REF] Mcc | Saudi Arabian Archaeological Reconnaissance 1976. Preliminary Report on the First Phase of the Comprehensive Archaeological Survey Program[END_REF].

Methods and List of Visited Sites

We based our field survey on the previous and published reports mentioned above and on the very good knowledge of the region of Mohammed and AbdelRahman, the assistants of Khalifah AL-Rowaili (director of antiquities in Qurayyât). We also benefited of the knowledge of local inhabitants and landowners: in Ithrâ, AbdulKarim al-Muzhein and Abu Tayeb, and in al-Hadîthah, and for the Jordanian border area, Abu Naif Falah Mensi Sarari. We spent a lot of time searching ancient inscriptions (Greek and Latin), particularly in private collections of folk art and archaeology, that of Awad al-Jbab displayed in Alghobain Resort (South Qurayyât) and in a private collection of local handicrafts in Qurayyât city, but finally we didn't find any. However, we warmly thank the owners for their welcome (Fig. 4 -Pl. 2).

Eventually we visited and documented 14 different sites in the Upper Wâdî as-Sirhân and Qurayyât vicinity and we isolated 36 spots, areas and monuments. The GPS coordinates of the sites were surveyed and placed on a map created from GoogleEarth photographs (Fig. 5 -Pl. 2). We noticed three main areas of ancient settlements. The first one extends to the east fringe of the northern part of the Wâdî as-Sirhân and includes Kâf (sites Kaf01 to Kaf09), Ithrâ (Ith01 to Ith08) and other villages and sites located between Kâf, Ithrâ and Qurayyât (Rad01, Wsh01 to Wsh03, Qar01 and 02, Min01 and 02). The second area gathers, further north, al-Hadîthah Village (Had01 to Had05) and other sites in the Jordanian border area (Cha01 and Rsh01). Most of these villages and archaeological spots were already surveyed by at least one of the previous expeditions. The third surveyed area is located further south within the Wâdî as-Sirhân. We spotted on Google Map then visited on the field a place called Gharb al-Qaidat (Qai01) where lies architectural remains of an ancient and extended occupation. This site caught our attention because the remains and their organization looked similar to that of the Christian settlement of Kilwa which was studied in the 1990s by Saba Fares (2010). Compared to the previous surveys, a new element comes into play that has profoundly transformed the landscape of the region. It is the recent construction of a large road connecting Qurayyât to Turaif and the Persian Gulf, and passing through Kâf and Ithrâ, which is likely to cover or have destroyed remains over about seventy meters (corresponding to the width of the road and sidewalks). The road facilitated our travels but made it difficult to find certain sites mentioned by our predecessors.

In the Eastern Area

In the Southern Area

On the eastern edge of the Wâdî as-Sirhân  Gharb al-Qaidat (Qai01), an impressive village 40 km south to Qurayyât. For all the sites and spots we engaged, when it was appropriate, an assessment of the state of conservation, a photographic coverage, production of 3D photogrammetric models, architectural description and plan drawings and sketches, a study of the chronological evolution of the remains using building archaeology methods, a surface collection of the ceramic and small items in order to date and feature the occupation periods. All the collected archaeological material has been bagged, inventoried, described and photographed, crated and entrusted to Kh. Al-Rowaili in Kâf on October 6 th 2021. A copy of the all the photographic documentation and a short preliminary report was given through an external Hard drive the same day to Saud Al-Tamemi for A. Zahrani in Riyadh.

Preliminary Observations and Synthesis

The most relevant sites and monuments are shortly described below within a preliminary synthesis gathering them according to the most obvious period of occupation.

Ancient and Pre-Classical Periods Sites

Most of the remains that stand out in the Upper Wâdî as-Sirhân 's landscape probably dates back to the Bronze and Iron Ages. However, some of the remains are older and the 1970s Saudi Arabian Archaeological Reconnaissance team discovered "Levantine Pre-Pottery Neolithic B" and provided images of many samples of the "earliest recognizable flint assemblages" found in Ithrâ vicinity (Adams et al. 1977: 34). In 1989, Parr very briefly evoked the presence of much prehistoric material (Parr 1989: 45). The 2018 Google Map survey as well as the 2021 field survey also recorded traces of an extended ancient occupation (Annex Document -last page). Numerous and well preserved small and monumental buildings, necropolis and graves, hamlets, villages and Desert Kites, were highlighted.

Desert Kite

On the field, we took the opportunity to start documenting two Desert Kites (masïada), which are monumental stone-made hunting structures and traps. (Haw03) did not provide archaeological material, but (Wsh01) (Fig. 6 -Pl. 3) provided flints and pottery sherds dated from the Bronze Age to the Umayyad Period. The latter was recorded by the 1976 field survey; the Saudi and American scholars published a sketch plan and longitudinal section of it (Adams et al. 1977: 35 and pl. 9-site 200-9) and described it as a penannular enclosure with long "tails" attached forming a gradually narrowing corridor leading to the entrance of the enclosure itself. Such devices are now well documented, and some Jordanian samples were dated to 7000 BC. (on this topic, Helms and Betts 1987 and more recently Abu-Azizeh and Tarawneh 2015; [START_REF] Crassard | Addressing the Desert Kites Phenomenon and Its Global Range Through a Multi-proxy Approach[END_REF][START_REF] Abu-Azizeh | Out of the Harra: Desert kites in Southeastern Jordan. New results from the South Eastern Badia Archaeological Project[END_REF].

Domestic, Military or Cultic Buildings

The most striking monument of the region is the so-called Qasr as-Sa'îdî, set on the top of the Jebel of the same name, which dominates the oasis and village of Kâf (Fig. 7 -Pl. 3). A ramp-like road (Kaf02) leads to the flat summit of the mountain. It is crowned by a citadel whom construction is not yet dated. According to the previous explorers, the eastern part of it could be very old, perhaps contemporary with the oldest occupation of the summit which could date back to the Bronze Age (Fig. 8 -Pl. 3). The northern, southern and western walls, much lower, could have been built, or reconstructed, by an Egyptian pilgrim from Port Said at the end of the 18 th century (Fig. 9 -Pl. 4) [START_REF] Winnett | Ancient Records from North Arabia[END_REF]Reed 1970: 62 andAl-Hussaini, Al-Muaikil et al., 2000: 78-90). The upper parts of the rampart were reconstructed, perhaps at the time of the pilgrim's work, and also more recently, in the 2010s, at the time of the enhancement of the site, installation of lighting, repair of the ramp etc. (Fig. 10 -Pl. 4). Only one gate, located on the eastern side of the surrounding wall, provides access to the summit plateau (Fig. 11 -Pl. 4). The door is made of blocs made in ancient (Roman and Byzantine) style, and it bears several Arabic Inscriptions (Fig. 12 -Pl. 5). It is flanked by two rectangular towers (Fig. 13 -Pl. 5). Four other square towers ensured the protection of the eastern slope, the most accessible. On a regular basis, small openings were made all along the rampart, on the base; this could have been arrow or shooting slits or water drainage holes. The summit today appears deserted (Kaf01); at first glance a very few constructions are visible. However, two main buildings are still visible. To the south, a one-room house, probably dating back to the Ottoman era or a more recent time, is preserved on almost all its height. To the north rises the rectangular building described by the Canadian explorers (Winnett and Reed 1970: 62) preserved to a height of about one meter (Fig. 14 -Pl. 5). It has been restored recently and that makes it difficult to study his architecture. Near it stands a circular reservoir (birkeh) and a possible cistern. Our general survey of the site made it possible to identify other occupation remains of occupation, such as possible ruined walls made of earth on a base of stones all around the rectangular main building, possible graves and possible evidences of funeral cremation further north with associate material dated to the Bronze or Iron Age period. In the middle of the plateau stand a ruined but still distinctive two-rooms building surrounded by Bronze or Iron Age sherds. Scattered on the plateau, a lot of pottery sherds are visible, however forms are scarce, probably since most of them have been collected during the previous surveys on the site. Consequently, most of the pottery sherds we collected are ordinary body-sherds, more difficult to interpret in terms of date, type and function. Nevertheless, P.-M. Blanc was able to connect the majority of them to the Middle and Recent Bronze and Iron Ages. Another important part dates to the Roman, Byzantine and Umayyad times. The Nabataean Period is not prominent; Medieval material is almost non-existent and Ottoman period attested by a few pottery sherds.

Another major monument was recently uncovered in Kâf. Located on the northern side of the main road, in the vicinity of a farm, it is referred to as Qasr Aqelat al-Mash'an (Kaf09) (Fig. 15 -Pl. 6). The site is mentioned in the most recent work regarding Kâf (Al-Hussaini, Al-Muaikil et al., 2000: 71-73). It has been unearthed in the end of the 1990s using a bulldozer by the landowner himself who was looking for a treasure. The rough excavation uncovered a huge building with thick walls (90 to 100 cm thick), regularly pierced with small windows (20 cm large, 48 high) placed at eye-level (Fig. 16 -Pl. 6). We collected a large amount of pottery sherds. Five or six fragments of grindstones are lying in the northern part of the building (Fig. 17 -Pl. 6). Most of the sherds date back to the first millennium BC, Iron Age or Hellenistic Period, a few to the Byzantine, Umayyad and Islamic eras. Against the southern wall of the building is a well full of sulphurous water. This well partly undermines the monument and threatens its stability. A few dozen meters from the Qasr, stand the remains of a possible extensive enclosure. Qasr Aqelat al-Mash'an (Fig. 18 -Pl. 7) could correspond to the so-called al-Uqayla Kâf, mentioned by Parr's team. It was described as "a flat site at the foot of the towering Jebel as-Sa'îdî" where the majority of picked up sherds "have close affinities with Iron Age II pottery (…) dating from the 7 th century BC." (Adams et al. 1977: 36).

As we can see, the site of Kâf presents different spots such as a citadel (Qasr as-Sa'îdî), a massive and fortified building (Aqelat al-Mash'an) and surrounding cemeteries. If these units belonged at least at one moment to a coherent whole, could Kâf be compared to the site of Qurayyah in the Hejâz for instance? Such comparisons are likely to help us, while waiting for excavations to be undertaken, to interpret the remains and understand their functions. The fortified plateau (mesa) of Qurayyah could has been "an ideal place for the celebration of highly relevant communal ceremonial and/or burial activities" (Luciani and Alsaud 2014: 141) and also a fortified place that "occasionally offered refuge for the population" [START_REF] Luciani | Quraya", Roads of Arabia[END_REF].

In Ithrâ, the remains of the Bronze and Iron Ages seem to be all concentrated on the top and slopes of the Jebel Radwa. The remains of a huge building are still visible on the foot of the northern slope of the Jebel (Fig. 19 -Pl. 7), separate from Râslaniyah district by the modern road. It is locally referred to as Qasr Kharab (Ith02). The pottery sherds collected belong to the Bronze or Iron Age periods, a very few to the Roman, Byzantine and early Islamic times. This site is mentioned by Adams et al. who date the majority of the sherds from the 7 th century BC" (Adams et al. 1977: 36).

Eventually, a Goggle Map survey lead us to undertake the visit of a site located further south in the eastern fringes of the Wâdî as-Sirhân (Fig. 20 -Pl. 7). Its general appearance and the dimension of the architectural units (Fig. 21 -Pl. 8) reminded to us the monastic settlement of Kilwa, located further west towards the Hejaz and recently studied [START_REF] Farès | L'inscription arabe de Kilwa : nouvelle lecture[END_REF]. Located 40 km to the south of Qurayyât, Gharb al-Qaidat (Qai01) is an extended village, today buried but still lying exposed on the surface many stone buildings (dwellings? Cells? Shops? Stores?), independent or semi-detached, alleys and also more elaborated complexes including enclosure (Fig. 22 -Pl. 8). We collected fiftyfour pottery sherds. The majority dates to the Bronze and Iron Period; a few to the Byzantine and Umayyad times, however, we didn't find among the remains evidence of a Christian settlement, such as engraved crosses or characteristic remains featuring a church for instance.

Cemeteries, Tombs and Graves

Numerous ancient graves and tombs are visible on Google Earth (Annex Document -last page). Winnett and Reed (1970: 62) mentioned Bronze Age graves in the vicinity of Kâf and Adams, Parr and their colleagues undertaken the excavation of an undisturbed stone cairn belonging to one of the cemeteries in the vicinity of Kâf (Adams et al. 1977: 36 and Pl. 9 -site 200-25). They uncovered with a skeleton two complete pottery jug and amphora attributed to the 7 th century BC.

On our side, we went to see several spots previously noticed thanks to Google Map or reported by the local colleagues. We picked up pottery and lithic material on the cemeteries that lie on the south-eastern and northern part of Kâf oasis (Kaf05 and 06, Fig. 23 -Pl. 8). To the north of the modern road built in the 1990s, we also found vestiges of graves (Kaf08) dated to the Bronze and Iron Ages. In the vicinity of Ithrâ, we noticed a silted up possible tomb with a trail on the top of Jebel Washwash (Wsh02) and we visited the huge necropolis on the foot, slope and top of the impressive and black Jebel Radwa (Rad01) mentioned above, that dominates Ithrâ oasis. The flat plateau is covered with stone-made tumulus and graves (Fig. 24 -Pl. 9). During a short half an hoursurvey, we found all around the best preserved circular building (Fig. 25 -Pl. 9) eleven inscribed stones in North Arabic and Nabataean scripts, but only three pottery sherds, dating back to the Bronze Age and the first Millennium BC. Another impressive site, Rashrâshîa (Rsh01), is visible further north, between al-Hadîthah village and the Jordanian border, to the east of the main modern road. It is an extensive rock art site including a cemetery. This site is known for his numerous rock drawings and inscriptions; several carved stones coming from this site are displayed today in the court of the modern fort of Kâf (Kaf03) (Fig. 26 -Pl. 10). The border area is a major smuggling point between Jordan and Arabia and is highly controlled. However, thanks to an authorization issued by the customs and accompanied by policemen, we visited the upper part of the site, identifying for instance a looted built tumulus, a pottery sherd from the bronze Age and an ancient bead made of white translucent stone.

So far, according to Parr, the occupation of the Wâdî as-Sirhân in ancient times mainly consisted of villages and burial grounds belonging to Transjordanian peoples and the major occupation of the area is dated approximately to the 7 th century Iron Age II (Parr 1989: 44-48 andAdams et al. 1977: 36). Many remains dated to the first millennium were recorded during our survey indeed. However, Pierre-Marie Blanc, and prior to him the archaeologists that surveyed the area in the 1990s (Al-Hussaini, [START_REF] Al-Hussaini | Documentation & Registration of Kâf Palace in Qurayyât[END_REF], identified also Bronze Age sherds in almost all the sites. Consequently, the study of the pottery (that has been recorded, described, drawn, photographed, and stored for this purpose) by a specialist of the Bronze and Iron ages periods is needed to provide a more accurate reconstruction of the Wâdî as-Sirhân ancient occupation.

Nabataean and Roman Times Occupation

It should be emphasized that while most of the visited sites provided pottery sherds dated back to the Nabataean and Roman period, architectural remains related to these periods are very scarce. The Nabataean sherds we found are characteristic, with the thin and red or orange ware, but we didn't find any painted sherds. Yet, in Ithrâ, Winnett and Reed wrote that they picked up "a number of Nabatean sherds of the beautiful, painted, 'egg-shell' ware" (Winnett and Reed 1970: 60). Furthermore, whereas we surveyed meticulously the eastern district of Ithrâ village called Râslaniyah (Ith04), we didn't find the remains of the possible sanctuary described by Winnett and Reed (Winnett and Reed 1970: 59-60). We looked for it all along the new main road linking Qurayyât to Turaif, also in the farm lying near the road and most of all everywhere in the recently abandoned equestrian centre associated to a house and a small mosque, built in the local traditional way -a base one-meter high built of stones, supporting walls in earth, then flat roof made of trunks and branches of palm trees and earth (fig. 27 -Pl. 10). However, already in 1977, Adams, Parr and their colleagues did not find this foundation and argued that they were "hidden beneath a recent building" (Adams et al. 1977: 36). Yet, the ground around the traditional house and the small mosque is particularly overshadowed by basaltic dust and loaded by archaeological material. We found there on the surface a large amount of ostrich egg fragments, at least twenty thin and unpainted Nabataean pottery sherds of small bowls -half is imported from Petra, half is local made. We also picked up seven lamp fragments dated to the Nabataean et Herodian periods (1 rst century BC-1 rst century AD), one lamp fragment dated to the late Hellenistic period, six Eastern Sigillata fragments (1srt and 2nd century AD), cultic stone vessel and stone slabs fragments bearing "Thamudic" or North Arabian inscriptions. All this material exactly corresponds to the material uncovered and described in 1962 by the Canadian scholars, which allowed them to interpret the architectural structure associated as an ancient sanctuary (fig. 28 -Pl. 10).

Eventually, we looked in vain, on sites and among private collectors in Qurayyât city, for Latin and Greek inscriptions. We didn't find the Nabataean inscription which was seen in the south side of Ithrâ oasis (Winnett and Reed 1970: 60, n°130: 160), but we documented eleven North Arabian (Thamudic) and Nabataean inscriptions, possibly unpublished, identified on the top of the Jebel Radwa. They are nowadays scattered all around the best-preserved circular tomb located at the northern extremity of the rock ridge overlooking the oasis (fig. 25). Regarding the Roman sherds found in small quantities in almost all the sites, they seem to be made in local, dark red ware.

Byzantine and Early Islamic (Umayyad and Abbasid) Periods

Ithrâ

The so-called Qasr in Ithrâ ( Ith01) is considered as one of the major architectural monuments of the northern province (Adams et al. 1977: 33). It is located to the north of the oasis and village. Winnett and Reed (1970: 59) provide a brief description, while Parr and co offered a first plan survey of it (Adams et al. 1977: 37 -Pl. 10. A, site 200-3). According to their report it was referred to as Qasr Ibrâhîm (Pl. 10. A) or Qasr Muhammad (p. 33). On our side we were referred to it as Qasr al-Nabati. Today it appears as an isolated building, however, the testimony of the previous explorers (Winnett and Reed 1970: 60) and our survey possibly identified other buildings further south, towards the centre of the modern village (Ith08). However, they are buried and it is difficult to distinguish them from the more recent and ruined and buried basalt walls of the village and enclosures of the oasis.

In the Qasr al-Nabati, there is numerous evidences of repair and re-occupation of the building, including recent ones, and evidences of clandestine excavations and vandalism. The monument is in serious danger of ruin.

Our survey allows us to describe the Qasr al-Nabati as a slightly trapezoidal square, massive and closed construction of 1100 m 2 , including four aisles surrounding a large courtyard; the four buildings are not perfectly perpendicular to each other ). The entrance is almost located in the middle of the eastern façade. The lintel of the main door supports an inscribed bloc that could have been placed in Medieval times ). The eastern and western aisles have deep rooms or rows of rooms accessible from the middle of their main façade. The northern and southern aisles have a series of small rooms each accessible from the courtyard (fig. 31-Pl. 12). The eastern, western and southern aisles at least have a second storey, however, we don't know yet where was located the staircase or the stair steps that were likely to led to the first floor. The southern building displays the most elegant façade and its second floor is the best preserved. An original decorative element is still visible: a face carved in relief (fig. 32-Pl. 12). The first floor of the western aisle includes a very characteristic facility of the Near East ancient architecture: a large room with troughs (fig. 33-Pl. 12). At least, nineteen troughs are preserved, still visible today, while according to Parr's plan (Adams et al. 1977: Pl. 10. A), there could have been twenty-three troughs. Old and more recent works (Villeneuve 1985(Villeneuve -1986;;[START_REF] Clauss-Balty | L'habitat dans les campagnes de Syrie du Sud aux époques classique et médiévale[END_REF]Baratte et al. forthcoming) undertaken about this facility elsewhere in the Near East allow to interpret most of them as stable troughs for horses, cows, camels or donkeys.

The northern aisle includes small rooms in row. The construction features meet perfectly those implemented in the well documented ancient buildings and dwellings of the Syrian and Jordanian Basaltic region of the Hawran (Vogüé 1865-1868[START_REF] Butler | Publication of the Princeton University Archaeological Expeditions to Syria in 1904-1905 and 1909[END_REF], Villeneuve 1985-1986, Clauss-Balty 2008, Piraud-Fournet forthcoming). Regularly the façades include a full course of bonding stones intended to bind the two faces of the walls. On the top of the walls, a course of corbels supported the roof made by jointed stone beams. Compared to the constructions of the Hawran, this building presents at least two particularities: on the one hand, there is no use of arches. For that reason, while the rooms can be long they remain narrow: around 3,5 m wide, to meet the strength constraints imposed by the basalt and the span of the beams placed on corbels. In fact, the architectural survey allowed to find the remains of only one arch, i.e. two pier capitals and at least height voussoirs. Most probably they belonged to the arch (4,5 m wide) that covered the entrance porch, opening to the courtyard. The arch's stones were reused in different reconstruction works within the Qasr. On the other hand, the presence of four aisles around the courtyard distinguishes it from the other possible farms already identified in the Hawran region. Almost all of them have only two or three aisles indeed. Four aisles buildings are scarce, usually identified as "palace" for official figures (such as the "Palace of Trajan" in Bostra, see P. Piraud-Fournet 2022), or military fort, or building linked with commercial activities such as caravanserai or inns. This building could be compared with other military buildings, such as the so-called Barracks at Umm el-Jimal for instance. Yet features like the large courtyard, numerous troughs in the stable and small rooms all around the courtyard, and by contrast the absence of specific defence devices, support the idea to see there a caravanserai, a hostel or lodge rather than a fort.

Various clues allow to suggest a date for the construction of the building. Whereas the local inhabitants referred to as "Nabataean", it was suggested that, in such a context, the word Nabati doesn't refer to a period but to a specific identity: The Arab identity as opposed to Byzantine, Ottoman or other cultures considered locally as exogenous (Valter 2002: 283-300, A, 7); thus Qasr al-Nabati should be translated as "huge old, local Arab building". Already in 1976, Parr and his colleagues suggested to date the construction of this monument to the Byzantine times because of its resemblance to the Syrian Hawran architecture (Adams et al. 1977: 37). And, indeed, we can argue that architectural practice consisting in inlaying all four courses an entire course of bonding stones in order to ensure the cohesion of the two facings of the wall and reinforce it, is considered to be implemented from the 5 th century onwards (Butler 1914, Piraud-Fournet forthcoming). Furthermore, according to Pierre-Marie Blanc and a comparison with Bostra's ancient buildings, the slightly curved appearance of the ashlars is also considered to be a feature of the Late Antiquity (Umayyad period). At least three carved Christian crosses were identified on doorposts, here and there in the building. Eventually, during the survey, we distinguished an ashlar of the southern external façade with a few words in Early Arabic scripts. The inscription is upside down and therefore illegible. This suggests that the ashlar is reused in the façade and supports even more the idea to date the construction of the building after the 6 th or 7 th century.

The environment of the building in ancient times is not clear. A well is still visible but it is located outside the courtyard, directly to the north of the Qasr. We also identified possible ancient walls further south but they are buried and it is not possible to compare or link them with the Qasr. The pottery found inside the Qasr (Ith01) and all around, in the old and abandoned village (Ith08) is quite homogeneous. We found in almost the same proportions pottery sherds dated to the Roman and Nabataean times and Umayyad and Abbasid periods. Sherds of the Byzantine Period are a little bit more numerous, and a very few pottery date back to the Ayyubid, Mameluke and Ottoman times.

Al-Hadîthah

Al-Hadîthah village is located further north, on the way to the Jordanian border. Winnett and Reed (1970: 64) wrote that they discovered at about half a mile south of al-Hadîthah the remains of an ancient irrigation channel constructed of basalt stones and mud-plaster; near the channel, they found sherds with green glaze of the mediaeval Arab period. They also mention the ruins of a "qasr" at about two miles south of the village and on a slight elevation not far away was an ancient cemetery with twelve graves and sherds of the Late Byzantine or Early Arab period. However, they did not document further any of these remains. We surveyed this extended village in order to find them, but we were not able to identified such buildings or pottery sherds among the ruins of the modern village made of stone and earth, the farms and cultivated gardens. On the other hand, thanks to the landowner Abu Naif, we discovered and photographed three portions of an ancient enclosure still visible on the surface, built with basalt ashlars and punctuated with buttresses (Had03 and 04) (fig. 34-Pl. 13). The wall is 0,85 m thick, the buttresses are about 0,80 m deep and 0,93 m wide. We were able to follow it for several meters in two different parts of the village. To the east, the enclosure is visible on 15 m long and had two buttresses. To the north, we followed 8,87 m of wall with one buttress, and on the east, 35 m of wall with two buttresses. Only two sherds were picked up in the vicinity of these buried portions of wall, belonging to the Early Islamic period. The most obvious comparison for this construction is the 'Ayn Sawda reservoir in Azraq located 200 km further north in Jordan [START_REF] Abu-Azizeh | Ayn Sawda reservoir project[END_REF]) dated to the same period.

To the south of the village, in the vicinity of a huge Housing complex built very recently for the numerous employees of the customs at the neighbor border, Abu Naif showed us the ruins of an ancient building. The remains of four rooms built with ashlars are lying on the slope of a small hill located to the east of the main road ). Almost fifty sherds were uncovered there, from the Nabataean to the Umayyad periods, the most of them dated to the Byzantine and Umayyad times.

As suggested by Abu Naif, we asked an authorization to the customs in order to visit some archaeological sites located in the border No man's land. We went to Rashrâshîa mentioned above and to a desert place called "Sharq al-Hadîtha" or Chaib el-Makhrooq (Cha01), an area located to the north of the village. We didn't find architectural remains there, however this was previously referred to as a ssettlement site and the eighty pottery sherds found dated to the Nabataean, Byzantine and Umayyad periods.

Minwa

Minwa is another abandoned oasis-village located between Kâf and Ithrâ. To the north of the village is a spot marked by ceramic scatters (Min01), dated to the Late Roman to Umayyad periods. Further north, outside of the village is a very large enclosure built of stones, possibly an ancient settlement site (Min02). Most of the pottery sherds uncovered on the ground surface date to the same periods.

Gharb al-Qaidat

Gharb al-Qaidat (Qai01) is the village identified through a Goggle Map survey and described above among the pre-classical settlements, since its architecture and pottery likely belong to Bronze or Iron Ages. However, a portion of the picked up pottery dates to the Byzantine and Umayyad times; it would be appropriate to investigate more in order to identify how this site was reoccupied at that time.

Some pottery sherds belonging to the Byzantine and Early Islamic (Umayyad and Abbasid) times are visible in almost all the sites of the area. The collection presents local (Hawran type well documented in Southern Syria) ware, as well as imported pottery such as Riley Amphorae, Bag shape Amphorae, Aqaba Amphora type and so on.

Medieval and Ottoman periods

Aside from a few amount of pottery sherds, the occupation in the Abbasid, Ayyubid and Mameluke periods is little represented. On the contrary, the late Ottoman occupation is well visible, with the fort of Kâf which was recently abundantly documented [START_REF] Al-Hussaini | Documentation & Registration of Kâf Palace in Qurayyât[END_REF] and reconstructed, with another recently reconstructed fort in Aïn Awas, and several abandoned oasesvillages made of earth, already mentioned above. Some of the ruined houses still display elaborated facilities, such as several buildings gathered by courtyards, toilets built within tower near the entrance, and columbaria in al-Hadîthah for instance . The mosques have two semidetached apses in the southern wall, for the mirhab and minbar. In Ithrâ and al-Hadîthah, a police fort is built on a hill overlooking the village. The old cemeteries, set away from the center of the villages, were recently enclosed by a wall. We also visited the almost completely abandoned salt extraction troughs (fig. 37-Pl. 14). They were dug in the extended sabkha areas, to the west of Ithrâ and the south of Kâf.

Near Qarqar, the Umm Ayyash massif is a geographical anomaly, a rocky resurgence emerging from the steppe. It has remained until recent years a local place of pilgrimage, for fertility rites. Not more than Winnett and Reed (1962) we found here archaeological remains, but a few rock drawings.

Eventually, we were shown in the gardens of Alghobain Resort (South Qurayyât) an old Arabic inscription that we photographed.

Conclusion

The field season allowed to document various identified monuments that had surprisingly been neglected so far. It also was an opportunity to explore other nearby sites and evaluate the potential of the comprehensive area in terms of heritage. The architectural inventory will raise an awareness of the importance of the archaeological sites disseminated and allow strategic plans for further possible fieldworks. It provides new elements for the understanding of the history of the area in Antiquity and later periods, up to modern times and paves the way for enhancement and touristic projects.

The Northern region of the Wâdî as-Sirhân has indeed a high potential in term of archaeological and heritage studies and research and in term of touristic activities. Comprehensive survey, study, consolidation and restoration of monuments such as the citadel of Jebel as-Sa'îdî and Aqelat al-Mashan in Kâf, and the Qasr al-Nabati in Ithrâ would be highly relevant. Furthermore, archaeological excavations would help to better analyse their architecture, date their construction and occupation phases, and provide material related to their function. Furthermore, the possible Nabataean temple in Râslaniyah-Ithrâ still has to be identified on the field, excavated, studied and enhanced.

A specific type of tourism could be developed in this area focusing on his majestic landscape. Hiking and not invasive walking tours punctuated by spots for view and archaeological sites, such as the desert kites, tombs with trail, villages, rock art and scripts, would help highlighting the original heritage and geography of the region. Another strength feature of this region is the oasis-villages. There is a need to protect the last farms and their gardens and ensure the cultivation, while restoring the traditional village houses to provide for instance sober and simple accommodations for tourists. Today, the main problem faced by the region is the looting activities, sometimes at great magnitude, carried out on all the sites. Almost every day, during our surveys, we saw looters. Their actions are very destructive, both for the knowledge and enhancement of the sites. Fighting against looting is probably the first action in which it is necessary to invest more; enhancing the sites and attracting tourists also can help protect their integrity. Eventually, the museum already existing in the modern fort of Kâf could be developed to display the ancient material linked to the sites of the area, the modern items already stored in the fort related to the nineteenth and twentieth life in Kâf.

ARCHITECTURAL SURVEY PROJECT ON THE NORTH-EASTERN MARGINS OF THE NABATAEAN KINGDOM (Annex)

Dr Tara STEIMER-HERBET January 2018

One of the aims of the project could be to focus on small-scale monuments, which are the main architectural remnants of Kaf and Ithra prehistorical and early historical populations. Many of these monuments served as tombs, commemorative markers and settlements. Ever since prehistoric times, the region of Kaf and Ithra was populated by highly, seasonally mobile human groups. Therefore, evidence for long-term occupations in the form of houses, village, accumulated living debris.

The marking of landscapes with small-scale monuments and the reconstruction of funerary practices are major research themes in archaeology [START_REF] Mccorriston | Gazetter of small-scale monuments in Prehistoric Hadramawt, Yemen: a radiocarbon chronology from the RASA-AHSD Project research 1996-2008[END_REF][START_REF] Steimer | Chraya: une nécropole de dolmens dans le Léja (Syrie du Sud)[END_REF]. Kaf and Ithra's rich heritage of monuments, high circular tower tombs with tails, settlements, jellyfish, kites, offers an interesting study set, bound to attract wider international interest. Monuments are not spatially distributed at random, but rather according to both resource availability and particular geographical specificities. The latter include the proximity of water, major communication axes, plants and stone sources, or -on a broader basis -a globally defensible position. Monuments were also erected in such a way to be understood by other communities familiar with the symbolic significance of both their form and positioning. As far as we know, they motioned not only economic value -through their association with strategic economic resources -but were also important social indicators to be understood by the people who built them, used them, appropriated, re-used them, visited them, and identified themselves to the latter, both culturally and territorially.

The study of an exhaustive panel of remains (burials, material culture, and settlements) as well as anthropological remains will provide the key to a detailed approach of the dynamics of evolution and adaptation of ancient inland populations at both local and regional levels. In this present study, we are particularly interested in analyzing temporal dynamics of spatial patterning.

Fig

  Fig. 1. Map of the Near East, location of the Wadi Sirhan in northern Saudi Arabia (P. P.-F. 2019)



  Ithrâ "Palace" (Ith01), Village (Ith08), and cemeteries (modern Ith05, and old Ith06)  Râslaniyah (Ith04)  The Salt troughs (Ith07)  Qasr al-Kharab (Ith02)  Eastern Mountain (Ith03) Between Ithrâ, Kâf and Qurayyât  Jebel Radwa 1 (Rad01)  Jebel Washwash (Wsh01, 02 and 03): a large kite, masïada (Wsh01), a modern cemetery (Wsh03) and the top of the Jebel (Wsh02)  Minwa (small enclosure Min01, large enclosure Min02)  Aïn al-Hawas (Haw01, 02, 03), a kite, a source, a fort etc.  Qarqar (Qar01)  Umm Ayyash (Qar02) Kâf Area  Jebel as-Sa'îdî (Kaf01 and 02)  Kâf Fort Museum (Kaf03)  Kâf Village (Kaf04)  Kâf northwest Necropolis (Kaf05)  Kâf south Necropolis (Kaf06)  Kâf old cemetery (Kaf07)  Kâf north Necropolis (Kaf08)  Aqelat al-Mashan (Kaf09) In the Northern Area Al-Hadîthah and the border Area  Al-Hadîthah, village (Had01)  Al-Hadîthah, cemetery (Had02)  Al-Hadîthah, northern wall of the reservoir (Had03)  Al-Hadîthah, eastern wall of the reservoir (Had04)  Al-Hadîthah, sud, "Housing Complex" (Had05)  Chaib al-Makhrooq (Sharq al-Hadîthah Cha01), remains and sherds  Rashrâshîa (Rsh01) in the Harra.

Fig. 3 .Fig

 3 Fig.3. The Qasr as-Sa'îdî in Kâf, watercolor (J.[START_REF] Euting | Tagebuch der Reise nach Syrien[END_REF]

Fig. 6 .

 6 Fig. 6. The "head" of the Jebel Washwash Desert Kite, from the top of Jebel Washwash 2 (P. P.-F. 2021)

Fig. 26 .

 26 Fig. 26. Modern Fort of Kâf. Ancient Carved stones coming from Rashrashia (P.-P. F. 2021)

Fig. 31 .

 31 Fig. 31. Ithrâ, the Qasr. The courtyard and the northern and eastern aisles (P.-P. F. 2021)

Fig. 34 .FigFig. 1 .

 341 Fig. 34. Al-Hadîthah. Ancient enclosure punctuated with buttresses (P.-P. F. 2021)

Fig. 2 .Fig. 3 .

 23 Fig. 2. The oasis-village of Ithrâ, in front of the Jebel Radwa. On the foreground, the top of the Jebel Washwash (P. P.-F. 2021) Fig. 3. The Qasr as-Sa'îdî in Kâf, watercolor (J. Euting 1883).

Fig. 4 .

 4 Fig. 4. The 2021 team of archaeologists (T. F. & P. P.-F. 2021).

Fig. 5 .

 5 Fig. 5. Map of the Qurayyât region, location of the three surveyed areas (T.-F. 2021).

Fig. 6 .

 6 Fig. 6. The "head" of the Jebel Washwash Desert Kite, from the top of Jebel Washwash 2 (P. P.-F. 2021).

Fig. 7 .

 7 Fig. 7. Aerial view of the Qasr as-Sa'îdî in Kâf (Google Map 2022).

Fig. 8 .

 8 Fig. 8. Sketch for the topographical survey of the citadel (T. F., P. P.-F., J. al-H. & S. al-T. 2021).

Fig. 9 .

 9 Fig. 9. The western rampart and the topographical survey by S. al-Tamemi and J. al-Harbi (P.-P. F. 2021).

Fig. 10 .

 10 Fig. 10. The eastern rampart (P.-P. F. 2021).

Fig. 11 .

 11 Fig. 11. The gate, from outside of the citadel (P.-P. F. 2021).

Fig. 12 .

 12 Fig. 12. The inscription on the gate (P.-P. F. 2021).

Fig. 13 .

 13 Fig. 13. The gate, from inside of the citadel (P.-P. F. 2021).

Fig. 14 .

 14 Fig. 14. The rectangular building on the top of the plateau (P.-P. F. 2021).

Fig. 15 .

 15 Fig. 15. Qasr Aqelat al-Mash'an from the top of Qasr as-Sa'îdî (P.-P. F. 2021).

Fig. 16 .

 16 Fig. 16. The south western corner of Qasr Aqelat al-Mash'an (P.-P. F. 2021).

Fig. 17 .

 17 Fig. 17. Fragments of grindstones in the northern part (P.-P. F. 2021).

Fig. 18 .

 18 Fig. 18. View inside the Qasr, towards the south and Qasr as-Sa'îdî (P.-P. F. 2021).

Fig. 19 .

 19 Fig. 19. Remains of a huge ancient building on the foot of the northern slope of the Jebel Radwa (P.-P. F. 2021).

Fig. 20 .

 20 Fig. 20. Gharb al-Qaidat, in the Wadi Sirhan. Aerial view of the site. (Google Map 2021).

Fig. 21 .

 21 Fig. 21. Gharb al-Qaidat, in the Wadi Sirhan. The site from the west (P.-P. F. 2021).

Fig. 22 .

 22 Fig. 22. Gharb al-Qaidat, in the Wadi Sirhan. Example of enclosed complex (P.-P. F. 2021).

Fig. 23 .

 23 Fig. 23. Kâf oasis. The south-eastern cemetery (T. F. 2021).

Fig. 24 .

 24 Fig. 24. Jebel Radwa. Stone made tumulus and graves on the top of the Jebel (P.-P. F. 2021).

Fig. 25 .

 25 Fig. 25. Jebel Radwa. Aerial view. Location of the best preserved circular funerary building and inscriptions (T. F. 2021).

Fig. 26 .

 26 Fig. 26. Modern Fort of Kâf. Ancient Carved stones coming from Rashrâshiâ. (P.-P. F. 2021).

Fig. 27 .

 27 Fig. 27. Ithrâ, Râslaniyah area. Basaltic dust area with archaeological material belonging to a possible ancient sanctuary (P.-P. F. 2021).

Fig. 28 .

 28 Fig. 28. Ithrâ, Râslaniyah area. Inscribed stone slabs fragments belonging to a possible ancient sanctuary (P.-P. F. 2021).

Fig. 29 .

 29 Fig. 29. Ithrâ, the Qasr. Layout made on the field, stone-by-stone survey, 1/50e (T. F. & P.-P. F. 2021).

Fig. 30 .

 30 Fig. 30. Ithrâ, the Qasr. The entrance gate and Medieval inscription (P.-P. F. 2021).

Fig. 31 .

 31 Fig. 31. Ithrâ, the Qasr. The courtyard and the northern and eastern aisles (P.-P. F. 2021).

Fig. 32 .

 32 Fig. 32. Ithrâ, the Qasr. The façade of the southern aisle and the decorative carved face, from the courtyard (P.-P. F. 2021).

Fig. 33 .

 33 Fig. 33. Ithrâ, the Qasr. The narrow room with troughs within the eastern aisle (P.-P. F. 2021).

Fig. 34 .

 34 Fig. 34. Al-Hadîthah. Ancient enclosure punctuated with buttresses (P.-P. F. 2021).

Fig. 35 .

 35 Fig. 35. Al-Hadîthah. Ancient house near the modern housing complex built to the south of the village (P.-P. F. 2021).

Fig. 36 .

 36 Fig. 36. Al-Hadîthah, the old village. Columbarium in a traditional house built in earth (P.-P. F. 2021).

Fig. 37 .

 37 Fig. 37. Ithrâ vicinity. Old salt extraction troughs (P.-P. F. 2021).