City Walls. By the end of the fourth millennium B.C.E. defensive walls were a regular feature of Mesopotamian cities. Immediately flanking the right (west) bank of the Euphrates in north Syria, the Late Uruk period (circa 3300 - circa 3000 B.C.E.) site at Habuba Kabira (south) was a well-planned rectangular city enclosed on its three exposed sides by rectilinear sundried mud-brick walls. Along the length of the walls, which were about 3 meters (10 feet) thick, were nearly fifty protruding square defensive towers; two gates set among the defensive towers along the western wall provided overland entry into the city, which was otherwise accessible only from the river. During the Early Dynastic I period (circa 2900 - circa 2750 B.C.E.) the wall enclosing Uruk, a city in southern Mesopotamia some thirty times the size of Habuba Kabira, was 9.5 kilometers (6 miles) long...