John Noble Wilford in The New York Times:
Archaeologists have embarked on excavations in northern Syria expected to widen and deepen understanding of a prehistoric culture in Mesopotamia that set the stage for the rise of the world’s first cities and states and the invention of writing. In two seasons of preliminary surveying and digging at the site known as Tell Zeidan, American and Syrian investigators have already uncovered a tantalizing sampling of artifacts from what had been a robust pre-urban settlement on the upper Euphrates River. People occupied the site for two millenniums, until 4000 B.C. — a little-known but fateful period of human cultural evolution.
Scholars of antiquity say that Zeidan should reveal insights into life in a time called the Ubaid period, 5500 to 4000 B.C. In those poorly studied centuries, irrigation agriculture became widespread, long-distance trade grew in influence socially and economically, powerful political leaders came to the fore and communities gradually divided into social classes of wealthy elites and poorer commoners.