The Oriental Institute and Argonne are jointly developing models of the settlement systems of the rain-fed and irrigated zones of Syria and Iraq, using the household as a fundamental modeling unit. The ancient urban dynamics of these two regions result from both geographic and cultural interconnections that will be represented at various scales and levels of resolution.

The basic objective of the rain-fed zone model is to allow for the scaling up of a settlement from a single household to a village, and ultimately to an urban center with its appropriate array of subsidiary and neighboring settlements. Agrarian production (specifically in light of environmental stresses) and social interaction will be modeled at a mutually consistent, fairly detailed level that will support a realistic representation of feedback processes, nonlinear behavior mechanisms, and some degree of self-organization in Bronze Age settlement systems. Emphasis will be on the development of the household model and its transformation into higher-order settlements. Everyday decisions in farming (e.g., when to plant, whether to fallow or crop annually, etc.) that are essential to community survival, as well as social factors such as the pooling of resources, are being incorporated. Moreover, the full model will include mechanisms that allow for the growth of social differentiation and that enable some households to grow and others to become subordinate.

In southern Iraq, the presence of a network of anastamosing rivers and engineered distributive canals makes for a markedly different cultural landscape than the rain-fed north. The rich patchwork of environments in the south not only supplies a rich subsistence base but also provides a convenient "low-friction" means of distribution of surpluses. Influences of environmental stresses, population changes, and resource competition will be included in the model, particularly as these relate to impacts on settlement patterns in the north.

The Argonne modeling framework has a proven record concerning the manipulation of a wide range of socio-economic and environmental data and is ideally suited to the analysis of data from ancient agriculture, social and demographic structure, environmental conditions, and the economy. In order to model the basic Bronze Age Mesopotamian subsistence economy, appropriate input data are required. Some of these data have been compiled through an earlier research initiative. The types of input data required include modern environmental data such as climate statistics and soil parameters, information on specific agricultural practices, major crop types and their contribution to the diet, field size and shape, as well as information concerning pastoralism, animal husbandry, flock size, and plough teams. Special practices, such as the grazing of flocks on green crops during a bad year, the harvesting of cereals when green, the removal of cereal chaff for temper of mud brick and plaster, and the use of secondary products for wool, manure, etc., are all complications in the local economical cycle that can be incorporated into the modeling framework. Overall, the combination of archaeobotanical, archaeozoological, cuneiform, and traditional data sources provides a wealth of information that can be used as inputs into the model to provide a very high degree of simulation fidelity.

Various outcomes of the proposed model will be tested against the record of the archaeological landscape derived from earlier surveys, remote sensing, and geographical information systems that bring together the various forms of settlement and environmental data into a single analytical framework.
We have initiated our modeling representation during the early village stage of settlement when simple cultivation techniques enabled modest levels of agricultural production. Archaeological surveys indicating the distribution of prehistoric villages and Bronze Age towns provide data sets against which the model can be tested. Moreover, landscape data provided by surveys conducted in tandem with remote sensing provide insights into local communications (tracks to fields), inter-regional routes, intensity of cultivation in the form of fertilizing with settlement-derived organic refuse, and potential pasture, all of which enable the pattern of settlement, land use, and inter-regional communications to be described and compared to the model output.

The growth of a small cluster of households into a village, and eventually a small town, is an anticipated outcome of the modeling framework, but whether a large 100-hectare city results from the modeling framework is an open question. At present, we anticipate that for the rain-fed zone, two levels of settlement scale will emerge from the modeling. First, input data may enable settlement size to increase to attain that of a small town of some 10-20 hectares. After this, a threshold may have to be crossed before settlement could increase rapidly to perhaps as much as 100 hectares, this being the approximate maximum size above which towns will not or cannot grow. This limit would represent a higher "emergent" state of the system, which perhaps may only be achieved if appropriate conditions are in operation. Such conditions presumably, but not necessarily, relate to the existence of all settlements within an interconnected network of communications along which flow goods, people, wealth, trade, and so on. Only when such settlement-driven networks were fully operative might we expect to see the higher threshold crossed, at which time settlements in the rain-fed zone might reach their maximum size. This size is conditioned by the capacity of the city region to sustain itself. Because in southern Iraq higher agricultural production and a network of 'lower friction' channels allows population size to exceed that of the northern cities, it is to be expected that settlements in the southern model will grow to exceed the critical 100- to 130-hectare threshold that apparently prevailed in the north. We therefore aim to focus our modeling within two operational modes:

• A basic "agrarian" mode in which a network of households / villages / small towns subsists on local food production, the products of small local flocks of sheep and goats, and minor exchange of staples and animals for other essentials. These settlements would be nested within a communication network of modest size that was in proportion to the scale of the settlement system itself.
• A more complex network mode in which the density of the communication network grows in proportion to the quantity and size of settlements. The local settlement system would develop within a larger interactive framework in the form of an autocatalytic set.

Whether such network-driven growth would enable settlement size to increase to the 100 hectare negative feedback threshold in the north and exceed it (owing to differences in the ‘friction coefficient’ of riverine networks) in the south remains to be determined.