The alluvial plains of southern Mesopotamia in the later half of the fourth millennium B.C. witnessed a immense expansion in the number of populated sites. Scholars still debate the reasons for this population increase, which seems to be too large to be explained simply by normal growth. One site, the city of Uruk, surpassed all others as an urban center surrounded by a group of secondary settlements. It covered approximately 250 hectares, or .96 square miles, and has been called “the first city in world history.” The site was dominated by large temple estates whose need for accounting and disbursing of revenues led to the recording of economic data on clay tablets. The city was ruled by a man depicted in art with many religious functions. He is often called a “priest-king.” Underneath this office was a stratified society in which certain professions were held in high esteem. One of the earliest written texts from Uruk provides a list of 120 officials including the leader of the city, leader of the law, leader of the plow, and leader of the lambs, as well as specialist terms for priests, metalworkers, potters, and others. Many other urban sites existed in southern Mesopotamia in close proximity to Uruk. To the east of southern Mesopotamia lay a region located below the Zagros Mountains called by modern scholars Susiana. The name reflects the civilization centered around the site of Susa. There temples were built and clay tablets, dating to about 100 years after the earliest tablets from Uruk, were inscribed with numerals and word-signs. Examples of Uruk-type pottery are found in Susiana as well as in other sites in the Zagros mountain region and in northern and central Iran, attesting to the important influence of Uruk upon writing and material culture. Uruk culture also spread into Syria and southern Turkey, where Uruk-style buildings were constructed in urban settlements.