Mesopotamia is located on the fertile flood plain of the Tigris and Euphrates rivers in a hot desert ecology. Human settlements based on irrigation agriculture first appeared coincident to the establishment of Eridu about 7400 BP. A great stepped tower, a ziggurat, which culminated a series of 20 structures built one upon another during a span of 3500 years evidences Eridu's importance. Public architectural monuments were the focus of early Mesopotamian community centers. By 6500 BP. large scale canal systems and many towns with public architecture had been founded. Eridu was the largest.

The Eridu period was followed by the Uruk, named for its largest and most impressive city. Settled by 6000 BP, Uruk grew to a population of 10,000 within a millennia. A significant number of developments occur in Mesopotamia during the Uruk period, including increased economic specialization, the introduction of metals, and use of beasts of burden, the wheel, cart and implements like the plow. River based exchange networks existed. Uruk's large and impressive Anu ziggurat was repeatedly enlarged to become Mesopotamia's largest.

During the dynastic period (5600 - 5100 BP.) a dozen city states evolved coincident with a widespread abandonment of rural settlement in the region. The population of Uruk rose to about 50,000 people and sprawled to cover 450 hectares, making it the world's first known urban center. Defensive walls around urban concentrations appeared.

A significant new development during the Dynastic period was clay tablets with written script dating to 5,400 BP. A developed system with presentation conventions and 1500 ideographic and pictographic elements evolved. The Sumerian symbols can be equated with the forms of the earlier token convention dated to 10,000 BP. Writing facilitated cultural continuity, community organization and commodity transaction. During this period, about 5,000 BP., the first recognizable states appeared.

The innovation of irrigation agriculture made possible human settlement and population expansion in otherwise inhospitable areas. Mesopotamia exemplifies this emergent phenomena and provides one of the earliest case studies of a circumscribed marginal ecology being transformed into a breadbasket supporting large population centers. Only the Nile river exhibits a parallel situation and parallel developments during the same epoch. In Mesopotamia the earliest period of occupation by irrigation based agriculturalists centers on Eridu. Previous agricultural communities existed in northern Mesopotamia where rainfall adequate to support crops and domesticated animals occurs. What is unique at Eridu and other southern Mesopotamian settlements is a dependence on canal based irrigation, allowing emergent agriculturalists to adapt to an otherwise inhospitable ecology.

Irrigation did occur elsewhere prior to Eridu's settlement. At Eridu irrigation is a community scale enterprise. The earliest occupational levels include significant, central public structures that evolved to ziggurats. These structures remained central to Mesopotamian communities and are probably reflective of the evolution of community and regional organization during a continuum spanning millennia. Their constant rebuilding and enlargement is indicative of their social significance. Their centrality in the community is not only spatial; they are surrounded by important architecture like storage buildings and the most palatial compounds.

Canal works and public architecture evidence community organization.

Evidence of land control or ownership systems is more ephemeral. Irrigation works make land more valuable to the agriculturalist or community, a quality dependent on a capacity to construct, operate and maintain a spatially complex, elaborate water transport system. This sort of sophisticated sphere of activity involves foresight, feasibility understanding, good engineering, organized construction and, to insure continuity, constant control and maintenance; in other words a community organization with continuity. Did communities, families or individuals own the land?

The value added dimension of irrigation system construction must have altered the way humans interrelated with land, particularly regarding temporality of ownership. Creators tend to view their products as property and persons and communities in creating extensive canal irrigation works became property owners. The ever larger central mound surmounted with community structures as the locus of the community area represents a form of deed, evidencing the community's longstanding claim to the locality.

Today the ziggurats, tells and canal works remain as evidence from which the archaeologist works to reconstruct how the complex web of the first civilization and urban area evolved from a highly successful adaptation of irrigation agriculture.

The combination of agriculture, complex large scale irrigation works and community organization was such a successful adaptation that it sustained 50,000 member urban centers. The massive ziggurats, manifestations of the community's heritage and enduring temporality, encase many chapters in the history of the evolution of Sumerian civilization and statehood. Ziggurats, tells, canals and defensive walls write history for us today as surely as did the Sumerians evolve to utilize writing, annote our most ancient histories and thereby begin to close the door on prehistory.