Nicolas Bernigaud

Alberte Bondeau

Joel Guiot

Frédérique Bertoncello

Marie-Jeanne Ouriachi

Loup Bernard

Delphine Isoardi

Philippe Leveau

Simulating the viability and profitability of Roman farms and villas in Southern Gaul by an agent-based model

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

Introduction

• For more than a century, the negative role of climate cooling in late antiquity has been discussed on a fall in agricultural yields and the decline of the Roman Empire (HUNTINGTON 1917;BÜNTGEN et al. 2016) • More recently, the evidence of global warming at the beginning of the Roman period (MCCORMICK et al. 2012) suggests now that climate may have been very favorable to the development of the Roman Empire around the beginning of our era (HARPER 2017).

• However, these interpretations are controversial as it remains difficult to perceive from historical and archaeological sources what the actual impact of these climatic variations may have been on yields.

• Modelling now offers the opportunity to design complex models and test different hypotheses • The model displays a map similar than the repartition of archeological data, but some differences are noticeable. For the 1 st c.

A.D. the potential appears good for olive groves in several area where archeological data are lacking: Digne/Riez area, languedocian coast, etc.

• Is importance of roman oleiculture still underrated by archaeological researches in these areas ?

• Or is it an artifact of the model ?

Archaeological testimony for olive-oil production

Conclusion

▪ The ROMCLIM agent-based model validates the hypothesis of a significant impact of the so-called "Roman Climate Optimum" on the productivity and profitability of agricultural exploitations and thus on the roman economy in general ▪ According to our model, climatic conditions were already favorable as early as the 2 nd century BC in Gaul to the development of commercial agriculture. But historically, it did not develop until the 1 st c. BC, after the Roman conquest ▪ The model also shows a negative impact on the profitability of agricultural exploitations during Late Antiquity/early Middle Ages (4 th -7 th c. AD), but the decrease appears not particularly strong for wheat production.

▪ The idea of a collapse of agriculture in Late Antiquity due to the cooling of the climate (cf HARPER 2017, BÜNTGEN et al. 2012) has been maybe exaggerated.

▪ One of the interesting results of this model is to show that climate change hasn't the same effect on the different cultures. We can see here that olive and wine are more sensitive to these changes than the wheat. In other words, agricultural subsistence is less impacted by climate than commercial productions. But if the agricultural system is 100% turned toward speculative agriculture, the change can create a societal collapse indeed.

  MARGARITELLI et al. 2020 Evolution of the surface temperature of the Mediterranean sea over the past 5500 years "In all of Gallia Narbonensis, the agricultural products are exactly the same as in Italy, while as one advances north toward the Cévennes, one no longer sees olive or fig trees; the other crops, it is true, continue to thrive, but, if one advances a bit more in the same direction, one sees that grape vines, in turn, only grow with great difficulty." Strabo (Geography, IV, 1) Study area : Gallia Narbonensis The ROMCLIM agent-based model ▪ Simulates the potential yields for wheat, wine and olives (agrosystemic emulator) ▪ Calculates the benefits of different types of villas and farms producing these crops in function of climatic and economics factors ▪ Model works for each century between 6 th c. BC and 7 th c. AD• Every "patch" sprouts each type of agent : wheat farm, olive grove,

▪▪▪▪•

  Price of 4 denarius/sextarius ▪ Price of 8 denarius/sextarius wich is the maximum for the price of vini rustici in Diocletian TRANSPORT COSTS on roman villas and farms profitability Simulation of wineries' profits in 3 rd c. AD ▪ Transport costs = 0 (top) ▪ Transport costs = 0.8 sesterces/kg/km (bottom) Simulation of wineries' profits in 3 rd c. AD ▪ Negative effect of an increase of + 1,5 °C in summer temperature on wineries' profits ▪ Decrease of the sum of profits from 451 to 184 millions of sestertius Wineries' groves /climate of 6 th c. BC vs 1 st c. AD ➢ Higher profitability of olive groves in the 1 st c. AD compared to 6 th c. BC , noticeably in the languedocian hinterland ▪ Olive oil price = 6 denarius/sextarius ▪ Transport costs = 0.2 sesterces/km/kg ▪ Area cultivated = 240 jugera (60 ha) 6 th c. BC vs 1 st c. AD ➢ Higher profitability of wineries in the 1 st c. AD (451 millions sestertius) compared to 6 th c. BC (288 millions sestertius), noticeably in the middle Rhone Valley Wine farms /climate of 6 th c. BC vs 1 st c. AD ➢ Increase in the profitability of wheat farms in the 1 st c./6 th c. BC appear very less important (0,04 %) Higher profitability for the productions according to the climate of the 1 st c. AD (bellow) /6 th BC (top) ▪ Model produces a virtual land use map with areas specialized in a specific type of production Wheat farms' profits Increase of potential benefits since 6 th c. until 2 nd c. BC which marks an important peak ▪ Highest level during late Iron Age and Roman period (2 nd peak in 3 rd c. AD) ▪ Decrease during Late Antiquity (4 th -7 th c. AD) ▪ Wheat is less sensitive to climate change than wine and olive productionOutput of the model: potential benefits (in millions sestertius) According archaeological data, roman olive growing was important in Provence, especially in the Var region. But some data indicate also this activity in the languedocian hinterland(LEVEAU 2003)

Legend Select a century between 2500 BP and 1300 BP LPJmL emulator : modify seasonal temperature and precipitations Modify selling price of olive oil, wine and wheat Benefits of wineries, olive groves and wheat farms in sesterces Size of each square which represents an agent is proportional to the benefits Agents : Wheat farm Olive grove Winerie Number of farmers

		6	13	14
	Cultivated area	0-2 ha	240 jugera (60 ha) (Caton)	100 jugera (25 ha)
				(Columelle)
	Yields	Returned by LPJmL emulator calculation/climate
	Harvest		Cultivated area * LPJmL yield
	Price of harvest	0-100 denarius/modius*	0-40 denarius/sextarius**	0-30 denarius/sextarius**
	Costs of exploitations	Quantity of grain necessary	Number of persons * 140	140 sesterces/year/slave
		for feed the family +	sesterces/year
		necessary seed for next year

Distance to the nearest capital of city Calculated by the model

	Main characteristics of the agents:
	Cost of transports	0-1 sesterce/kg/km * Distance to the nearest capital
	Benefits	Surplus price -costs	Harvest price -costs
	Action	Disappear if annual harvest	Disappear if benefits < 0
		can't feed the family

Cereal/Pul ses Price* Wines Price** Olive oil Price**

	Wheat	100	Piceni	30	Olei floris 40
	Barley	60	Rhosati	20	Olei	24
					sequentis
	Lentil	100	Vini	8	Olei cibari 24
			Rustici
			Zythi	2	Olei	8
					raphanini
	*	denarius/modius
	**	denarius/sextarius

th c. BC 3 rd c. BC 2 nd c. BC 4 th c. AD 1 st c. AD 7 th c. AD Iron Age High Empire Late Antiquity

		Archaeological testimonies of roman
		oleiculture
	Conclusion	Numerous data Sporadic data
		▪ Agent-based model RomClim coupled with
		agrosystemic model shows that the Roman Climate
		Optimum has had probably a strong and favorable
		impact on wine production and olive growing, but not
		so much on wheat production
	6	LEVEAU 2003 ▪ RCO was most beneficial for viticulture than others
		crops
		▪ The strong economical development of Gallia
		Narbonensis in High Empire was supported by the
		development of the villa system (agricultural rentier)
		largely invested in wine production
		▪ But why the takeoff of this economy don't start more
		frankly in the 1st c. BC, where climatic conditions
		Higher where already good ?
		Olives groves' profits
		Lower	30

5th c. BC Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 14 2300 BP 4th c. BC Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 15 2200 BP 3rd c. BC Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 16 2100 BP 2nd c. BC Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 17 2000 BP 1st c. BC Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 18 1900 BP 1st c. AD Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 19 1800 BP 2nd c. AD Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 20 1700 BP 3rd c. AD Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 21 1600 BP 4th c. AD Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 22 1500 BP 5th c. AD Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 23 1400 BP 6th c. AD Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city 24 1300 BP 7th c. AD Benefits of wheat farms Benefits of olive groves Benefits of wineries Roman capital of city