Marcos Such-Gutiérrez/National Geographic:

The foundations of human civilization first flowered in the fertile lands between the Euphrates and Tigris Rivers. Known today as Sumer, this ground-breaking culture gave birth to not only the first cities but also innovations in transportation, literature, and monumental architecture.
For more than 2,000 years, Sumerian culture flourished and was the dominant power in Mesopotamia. Across the region that is now southern Iraq, powerful city-states emerged, towering ziggurats rose, sweeping epics were told, and golden jewelry adorned the rich and powerful. Dominance and control would shift among its glorious cities as the years rolled by. The civilization reached its peak in the late third millennium B.C and then gradually fell away. Sumerian civilization and its achievements would be forgotten for millennia, until archaeologists began exploring the region in earnest in the 19th and 20th centuries. Glorious finds in the area revealed the richness and complexity of this ancient culture and allowed scholars to see how Sumerian influences cascaded through the civilizations that followed it.
CITIES OF SUMER
In the third millennium B.C. at least a dozen large independent city-states existed within the territory of Sumer. These included Kish, Uruk, Ur, Nippur, Umma, and Lagash. Each of these walled urban centers controlled the surrounding lands and villages. Inside each city stood a large temple dedicated to a particular divinity, and served as the focal point of city life.
Cities and kings
Settlers arrived in the Mesopotamian floodplain around the sixth millennium B.C. These innovators devised an irrigation system of canals to harness the waters of the Tigris and Euphrates and better manage agriculture in the region. Their success created rich agricultural centers of trade. The wealth turned settlements into villages, and villages grew into cities with thousands of residents.
By 3500 B.C., Sumer had grown into a collection of city-states linked by linguistic and religious traditions. Among the most significant were Eridu, Uruk, Ur, Larsa, Isin, Adab, Lagash, Nippur, and Kish. Over time, some of them grew more powerful than others, and for brief periods, one city-state might rule the others until it fell from power. The Bible mentions Sumerian cities and rulers: “The beginning of his kingdom was Babel, Erech, and Accad, all of them in the land of Shinar. From that land he went into Assyria, and built Nineveh, Rehobothir, Calah,and Resen between Nineveh and Calah; that is the great city” (Genesis 10:10-12).
These cities were ruled by kings, whose names might have been forgotten were it not for the discovery of the Sumerian King List. Copies of the list have been found on 16 different clay tablets or cylinders found across Mesopotamia. The most complete one features the names of prominent cities, their rulers, and how long they ruled. Scholars are quick to point out that the Sumerian King List blends legend and history, with the earliest kings enjoying excessively long reigns and the more recent having human-size lengths of time on the throne.
Rise of Uruk
The very first city-state to rise to prominence was Uruk (called “Erech” in the Bible). According to the Sumerian King List, it was founded by King Enmerkar around 4500 B.C. At its peak, Uruk numbered some 40,000 inhabitants—a huge population that drove significant economic development.
The city’s wealth was reflected in its monumental architecture. Uruk’s ziggurat, dedicated to the Sumerian sky god Anu, was completed by the late fourth millennium B.C. Topped with its White Temple, its soaring form, resplendent in sunshine, would have soared high many centuries before Egypt’s Great Pyramid.
Excavations in the 20th century by German archaeologists revealed Uruk’s richness, with evidence of large-scale gold-, silver-, and copper-working. Other massive structures were uncovered, including smaller brick temples and a defensive wall. Archaeologists recovered troves of clay tablets as well as works of art.
Scholars continued to piece together Sumerian history as other cities were excavated. In Lagash, a sophisticated irrigation and sluice system was found. The most famous discoveries were found by the British Museum’s Leonard Woolley and the University of Pennsylvania. They uncovered Ur, a city that peaked in the late third millennium B.C. Woolley’s digs of the 1920s and ’30s excavated Ur’s 80-foot-tall ziggurat dedicated to the moon god Nanna.
Woolley also discovered the city’s royal cemetery from the mid-third millennium B.C. These tombs held crowns, necklaces, and the exquisite box known as the Standard of Ur, inlaid with jeweled mosaics depicting scenes of war and booty. The tombs also contain the remains of royal servants sacrificed to continue “serving” their sovereigns beyond the grave.
Birth of writing
Sumer’s gifts to humanity are immeasurable. The word “Sumer” comes from shumerum, which was what the Akkadians, Sumer’s neighbors to the north, called the inhabitants of this area. The ancient Sumerians called themselves salmat qaqqadi, meaning “black heads.”
Sumer’s agricultural successes led to a need for a methodical system of recording information. Sumerian merchants needed reliable ways to track their businesses.