The Sumerians were an agricultural people. They discovered how to irrigate vast areas of the hot, dry Mesopotamian plain. This enabled them to raise surplus crops to trade with other people of the Near East for metals, which Sumerian craftsmen were skilled at working and engraving, and probably with people of the Indus Valley for gemstones.
The Sumerians, one of the first peoples to live in cities, used dried clay or mud bricks for building. Their most important structure was the temple, built on a raised platform, which developed into a terraced tower, or ziggurat. Priests held great power and were sometimes the actual rulers. The Sumerians worshiped a number of gods; kings, who came to power usually as a result of military victories, were regarded as the gods' chosen representatives. Gilgamesh, a legendary Sumerian king deified after his death, became the hero of a Babylonian epic.
It is generally believed that the Sumerians migrated to Mesopotamia from the hills to the north before 3500 B.C. Sumer developed into a number of independent city-states that carried on almost continual warfare among themselves until united by Lugal-zaggisi, about 2350 B.C. A decade later they were conquered by the Akkadians, a Semitic people to the north, led by their king Sargon. The Akkadian Empire fell to the Guti, a tribe of northern barbarians, about 200 years later.
Sumer regained independence about 2135 B.C. Ur-Nammu established at the city of Ur a dynasty that ruled for more than 100 years, reunited Sumer and Akkad, and built an empire stretching from Elam in the east to Assyria in the north.
About 2000 B.C., the Sumerian empire began to collapse from internal and external pressures. Akkad and Elam both revolted, and the Elamites invaded Sumer and sacked Ur. About the same time, the Amorites, a Semitic people, invaded from the west. They gained control of Mesopotamia and founded the empire of Babylonia. The Sumerians soon ceased to exist as a separate people.