Sumer was the southernmost region of ancient Mesopotamia (modern-day southern Iraq and parts of Kuwait), which has long been considered the cradle of civilization. The name comes from Akkadian, the language of the north of Mesopotamia, and means "land of the civilized kings." Sumer is recognized as the birthplace of many of the 'firsts' of civilization, including writing and the development of the city.

The Sumerians called themselves "the black-headed people," and their land, in cuneiform script, was simply "the land" or "the land of the black-headed people," and, in the biblical Book of Genesis, Sumer is known as Shinar. According to the Sumerian King List, when the gods first gave human beings the gifts necessary for cultivating society, they did so by establishing the city of Eridu in the region of Sumer. While the Sumerian city of Uruk is held to be the oldest city in the world, the ancient Mesopotamians believed that it was Eridu and that it was here that order was established and civilization began.

The region of Sumer was long thought to have been first inhabited around 5000 BCE. This date has been contested in recent years, however, and it is now thought that human activity in the area began much earlier. The first settlers were not Sumerians but a people of unknown origin whom archaeologists have termed the Ubaid people – from the excavated mound of al-Ubaid, where the artifacts were uncovered that first attested to their existence – or the Proto-Euphrateans, which designates them as earlier inhabitants of the region of the Euphrates River.

Whoever these people were, they had already moved from a hunter-gatherer society to an agrarian one during the Ubaid period of circa 6500 to 4000 BCE. Excavations from al-Ubaid and other sites throughout southern Iraq have uncovered stone tools from the Ubaid people, such as hoes, knives, and adzes, and clay artifacts which included sickles, bricks, painted pottery, and figurines. These people were the first agents of civilization in the region. At what point the people who came to be known as Sumerians entered the area is not known.

According to scholar Samuel Noah Kramer:

The first ruler of Sumer, whose deeds are recorded, if only in the briefest kind of statement, is a king by the name of Etana of Kish, who may have come to the throne quite early in the third millennium B.C. In the King List he is described as he who stabilized all the lands.

(Sumerians, 43)

The semimythical Sumerian King List (abbreviated as SKL) is a cuneiform document, written by a scribe of the city of Lagash, at some point during the Ur III period (circa 2112 to circa 2004 BCE, probably around 2100 BCE) which lists all of the kings of the region, and their accomplishments, in an attempt to show continuity of order in society as expressed through kingship dating back to the beginning of civilization at Eridu.

As the Mesopotamians generally, and the Sumerians specifically, believed that civilization was the result of the gods' triumph of order over chaos, the SKL is thought to have been created to legitimize the reign of a king named Utu-Hegal (reign circa 2119 to circa 2112 BCE) by showing him as the most recent in a long line of rulers of the region. The SKL includes King Etana, the central character in the Myth of Etana, which tells the story of his ascent to heaven on the back of an eagle and, like other kings mentioned in the list (Dumuzi and Gilgamesh among them), was known for superhuman feats and heroism.

Utu-Hegal, it is thought, was trying to link himself to such earlier hero-kings through the creation of the SKL. Since the Mesopotamians believed that the gods had set everything in motion, and that human beings were created as co-laborers with the gods to maintain order and hold back chaos, the early writers of history in the region focused on the link between their rulers and their gods, as expressed in the SKL, which attempts to show an unbroken succession of kingship from the first king of Eridu down through the Isin-Larsa period.

The SKL is not considered a reliable primary source, however, and writing down the history of human accomplishments seems to have been considered a matter of little importance for the earliest Sumerian scribes. As a result, the early history of Sumer has been deduced from the archaeological and geological record more than a written tradition, and much information is still unavailable to modern scholars.

Whenever the Sumerian civilization was first established in the region, by 3600 BCE, they had invented the wheel, writing, the sailboat, agricultural processes such as irrigation, and the concept of the city. Although China and the Indus Valley Civilization also lay claim to the honor of "the first cities" in the world, it is generally accepted that the earliest cities rose in Sumer and, among the most important, were Eridu, Uruk, Ur, Larsa, Isin, Adab, Kullah, Lagash, Nippur, and Kish.

It has been noted by scholars (Kramer, among others) that these names are not Sumerian but come from the Ubaid people and so were founded, at least as villages, during the Ubaid period, only developing into cities during the Uruk period (circa 4000 to 3100 BCE). Other cities in Sumer that developed during this time were Sippar, Shuruppak, Bad-tibira, Girsu, Umma, Urukag, Nina, and Kissura. All were of varying size and scope, with Uruk the largest and most powerful at its height.

With the establishment of the cities of Sumer, their history unfolds from approximately 4000 BCE to 1750 BCE, when the Sumerians ceased to exist as a people after Sumer was invaded by the Gutians, Elamites, and Amorites. Trade had been firmly established with foreign lands by the Uruk period, and writing evolved from pictograms to cuneiform script. It is thought that trade was the main motivator in the development of writing, as there now had to be some means for accurate, long-distance communication between the merchants of Sumer and their agents abroad.

The concept of kingship also arose at this time, and the city-states of Sumer were each ruled by a monarch who was assisted by a council of elders (which included both men and women). According to Kramer, the kings following Etana were Semites, not Sumerians, as attested to by their names, such as Enmebaraggesi of Kish. It is not until after the rule of eight kings passed that Sumerian names begin to appear in the SKL.

The Early Dynastic period in Mesopotamia (circa 2900 to circa 2350/2334 BCE) saw the subtle shift from a priest-king (known as an ensi) to a more modern-day concept of king, known as a lugal ("big man"). The city-states of Sumer during this time fought for control of arable land and water rights until the rise of the First Dynasty of Lagash circa 2500 BCE. Under their king Eannutum, Lagash became the centre of a small empire, which included most of Sumer and parts of neighboring Elam.

This empire was still extant under the king Lugal-Zage when a young man, who later claimed to have been the king's gardener, seized the throne. This was Sargon of Akkad, who would go on to found the Akkadian Empire (2350/2334 to 2154 BCE), the first multinational empire in the world and, it is thought, based on the model set by Eannutum.

The Akkadian Empire ruled over the majority of Mesopotamia, including Sumer, until a people known as the Gutians invaded from the north (the area of modern-day Iran) and destroyed the major cities. The Gutian period (circa 2141 to circa 2050 BCE) is considered a dark age in Sumerian history, and the Gutians were universally reviled by Sumerian writers in later histories, most of which consider them a punishment sent by the gods. Historians continue to debate the claims of Sumerian scribes, however, and it is thought that climate change, rather than invasion, caused the fall of cities like Akkad or at least weakened them prior to invasion.

The last period in Sumerian history is known as the Ur III period, so-named for the Third Dynasty of the city of Ur. This period is also known as the Sumerian Renaissance due to the remarkable advances in culture, touching upon virtually every single aspect of civilized human life. The kings of Ur, Ur-Nammu (reign circa 2112 to circa 2094 BCE) and Shulgi (reign circa 2094 to circa 2046 BCE), set cultural advancement as the goal of their administrations and maintained peace, which allowed for art and technology to flourish. Whether invented before or during the Ur III period, the tools, concepts, and technological innovations in place during the Third Dynasty of Ur solidified the Sumerians' place in history as the creators of civilization, as recognized in the present.

In Samuel Noah Kramer's book History Begins at Sumer, he lists 39 'firsts' in history from the region among which are the first schools, the first proverbs and sayings, the first messiahs, the first Noah and the Flood stories, the first love song, the first aquarium, the first legal precedents in court cases, the first tale of a dying and resurrected god, the first funeral chants, first biblical parallels, and first moral ideas. The Sumerians also essentially invented time in that their sexigesimal system of counting (a system based on the number 60) created the 60-second minute and the 60-minute hour. They also divided the night and day into periods of 12 hours, set a limit on a workday, with a time for beginning and ending, and established the concept of days off for holidays. Scholar Stephen Bertman writes:

The hand of Mesopotamia still determines the hourly length of the traditional workday and even the length of our electronic entertainment (half-hour or hour TV shows) when our workday has stopped.

(334)

Bertman further notes that the modern-day practice of checking one's horoscope comes from ancient Sumer, and that the astrological signs one is born under were first noted and named by the ancient Mesopotamians.

Ur-Nammu wrote the first legal code in Sumer, which became the precedent for the much later and better-known Code of Hammurabi of Babylon. Scholar Paul Kriwaczek writes:

Ur-Nammu's universal legal pronouncements present a good example of the unifying drive of Ur's kings: the compulsion to regulate every aspect of life.

(149)

Sumer, under the unifying force of the Third Dynasty of Ur, became a patrimonial state ("meaning one constructed on the pattern of the patriarchal family ruled by a father figure", as Kriwaczek notes, 149) in which the monarch served as the father figure who guided his children along a proper path toward prosperity.

Ur-Nammu's son, Shulgi, is considered the greatest of the Neo-Sumerian kings, who continued his father's policies but went further. In an effort to both impress his people and distinguish himself from his father, Shulgi ran 200 miles (321.8 km) between the religious centre of Nippur and the capital city of Ur and back again – in one day – in order to officiate at the festivals in both cities. Though some have considered the hymn that recounts his achievement (A Praise Poem of Shulgi) as a kingly boast and highly exaggerated, scholars have determined that he could, in fact, have made his famous run, and, further, that it was in keeping with the spirit of Shulgi's rule. Creating a sense of awe and admiration in their subjects seems to have been central to the governing power of the kings of Ur at this time.

Under Shulgi's reign, a wall was constructed 155 miles (250 km) long to keep out the Semitic-speaking tribes known as the Martu or Tidnum, but better-known by their biblical name of Amorites. Shulgi's son, grandson, and great-grandson all renovated and strengthened the wall to keep those they referred to as "barbarians" out of Sumer proper, but the barrier proved ineffective. The wall could not be properly manned or maintained, and, further, it was not anchored to any solid barrier at the endpoints, and so invaders could simply follow the wall on one side to either endpoint and then walk around it, which is precisely what the Amorites did.

The forces of neighboring Elam breached the wall and marched on Ur, sacking it and carrying away the king circa 1750 BCE. The Amorites had already established themselves in the land, but with the fall of Ur and a severe famine resulting from climate change and the overuse of the land, many migrated south. Among these migrating Amorites, it is thought, was Abraham the patriarch, who left Mesopotamia to settle in the land of Canaan.

Following the Ur III period and the fall of Ur, many Sumerians migrated north. Sumerian was no longer spoken as a language (though it was still written), having been largely replaced by the Semitic Akkadian, and so Sumerian culture ended. Their legacy, however, continues in many aspects of civilization, which those in the modern day take for granted as having always existed. Everything begins somewhere, however, and a concept as basic to modern-day life as the 24-hour day was invented at some point in time and, as with so many other aspects of civilization, in Sumer.