Around 3000 BCE the city of Uruk, on a branch of the Euphrates in southern Iraq, covered roughly two and a half square kilometers or more, and the wall later built around it, which legend credited to its king Gilgamesh, enclosed more than five. Estimates of its population run from about 25,000 to 50,000 people. Around 3000 BCE, Uruk was probably the largest city in the world. No one had lived this way before: thousands of strangers packed together, most of them no longer growing their own food, depending on officials, temples and markets to feed them. Archaeologists give the name of this city to a whole age. The Uruk period ran from about 4000 to 3100 BCE, and during it the south of Mesopotamia became the first urban society on earth.

Why the south?

There is no single answer to why cities appeared here first. Rich irrigated soil produced large surpluses of barley, enough to feed people who did not farm. The marshes and rivers supplied fish, reeds and birds. The archaeologist Guillermo Algaze has stressed transport. In Algaze's view, cities first grew in the south because rivers made it cheap to move goods by boat. A boat could carry grain, wool or pottery far more cheaply than a donkey, so southern towns could trade with one another and draw in food from a wide area. Others stress religion or conflict, and most agree several forces worked together.

Houses of the gods

At Uruk's heart stood two great precincts. One, called Eanna, belonged to Inanna, goddess of love and war. The other honored An, the sky god, and held the so-called White Temple on a high platform, plastered so that it gleamed above the plain. For Sumerians, a temple was literally a god's house, where the divine statue was fed, clothed and served. Sumerians believed each city belonged to its patron god or goddess: Inanna at Uruk, Enlil at Nippur, Nanna the moon god at Ur. The temple also acted as a giant household that owned fields, herds and workshops.

Early twentieth century scholars, reading temple archives from the city of Lagash, built a "temple-state" theory in which the temple owned all the land and every citizen worked for the god. Further study and new tablets changed that picture. The temple-state theory has been revised: scholars now see temples as one of several landholders, alongside rulers, wealthy families and ordinary households.

Seals, bowls and the work of a city

City life needed new tools for keeping track of things. One was the cylinder seal, a small carved stone cylinder that left a continuous picture when rolled across wet clay. A cylinder seal was used to roll a mark of ownership or approval into clay, on jar stoppers, door locks, bundles of goods and later on tablets.

A humbler object tells as much. Archaeologists have found vast numbers of crude, thick-walled bowls with a slanted rim, made quickly in molds. They are among the most common finds of the age. Beveled-rim bowls were most likely used for handing out grain rations to workers, since their sizes cluster around a standard measure. If that reading is right, temples or rulers were feeding large numbers of laborers, perhaps in exchange for work on canals and buildings. The seals of the period also show captives with their arms bound, a reminder that some of that labor was not free.

The Uruk Vase and the Uruk world

The most famous object of the age is a tall alabaster vessel about a meter high, found in the Eanna precinct. The Uruk Vase shows a procession bringing offerings to the goddess Inanna. Its bands rise from water and crops at the bottom, through rows of animals and naked men carrying baskets and jars, to a scene at the top where a figure greets Inanna at her shrine. It reads as a picture of the whole order of society, with nature at the base, laborers in the middle and the gods at the top.

Uruk-style pottery, seals and buildings also appear far from the south, in Syria, southeastern Turkey and western Iran. At Habuba Kabira, on the Euphrates in Syria, a planned town with Uruk-style houses was built on land that had no long local history. Outposts such as Habuba Kabira most likely served trade for goods the south lacked, such as metal, timber and stone.

Worked example: What a cheap bowl can prove

Suppose you excavate a corner of an Uruk-period building and find a dump of several thousand broken beveled-rim bowls. What can you responsibly say? First, the bowls were made fast and thrown away freely, so they were not treasured goods. Second, their volumes cluster near a single size, which looks like a standard measure rather than random variation. Third, later tablets from the same region list daily rations of barley for workers in standard units. Put together, these clues support the ration theory: someone with authority was measuring out food to many people. Other explanations have been offered, such as molds for baking bread or vessels for offerings, and some bowls may have served those uses too. Even so, a pile of cheap pottery reveals something no royal monument would admit: a city like Uruk rested on the daily, measured labor of thousands of people whose names were never recorded.