Settlements were made in the fertile plain which had thus been won, and which, along with the adjoining desert, was called by the Sumerians the Edin, or “Plain.”  On the southern edge of this plain, and on what was then the coast-line of the Persian Gulf, the town of Eridu was built, which soon became a centre of maritime trade.  Its site is now marked by the mounds of Abu Shahrein or Nowawis, nearly 150 miles from the sea; its foundation, therefore, must go back to about 7500 years, or 5500 B.C.  Ur, a little to the north-west, with its temple of the Moon-god, was a colony of Eridu.

In the plain itself many cities were erected, which rose around the temples of the gods.  In the north was Nippur, now Niffer, whose great temple of Mul-lil or El-lil, the Lord of the Ghost-world, was a centre of Babylonian religion for unnumbered centuries.  After the Semitic conquest Mul-lil came to be addressed as Bel or “Lord,” and when the rise of Babylon caused the worship of its patron-deity Bel-Merodach to spread throughout the country, the Bel of Nippur became known as the “older Bel.”  Nippur was watered by the canal Kabaru, the Chebar of Ezekiel, and to the south of it was the city of Lagas, now Tello, where French excavators have brought to light an early seat of Sumerian power.  A little to the west of Lagas was Larsa, the modern Senkereh, famous for its ancient temple of the Sun-god, a few miles to the north-west of which stood Erech, now Warka, dedicated to the Sky-god Anu and his daughter Istar.

Northward of Nippur was Bab-ili or Babylon, “the Gate of God,” a Semitic translation of its original Sumerian name, Ka-Dimirra.  It was a double city, built on either side of the Euphrates, and adjoining its suburb of Borsippa, once an independent town.  Babylon seems to have been a colony of Eridu, and its god, Bel-Merodach, called by the Sumerians “Asari who does good to man,” was held to be the son of Ea, the culture-god of Eridu.  E-Saggil, the great temple of Bel-Merodach, rose in the midst of Babylon; the temple of Nebo, his “prophet” and interpreter, rose hard by in Borsippa.  Its ruins are now known as the Birs-i-Nimrud, in which travellers have seen the Tower of Babel.

In the neighbourhood of Babylon were Kish (El-Hymar) and Kutha (Tel-Ibrahim); somewhat to the north of it, and on the banks of the Euphrates, was Sippara or Sepharvaim, whose temple, dedicated to the Sun-god, has been found in the mounds of Abu-Habba.  Sippara was the northern fortress of the Babylonian plain; it stood where the Tigris and Euphrates approached most nearly one another, and where, therefore, the plain itself came practically to an end.  Upi or Opis, on the Tigris, still farther to the north, lay outside the boundaries of primaeval Chaldaea.

East of Babylonia were the mountains of Elam, inhabited by non-Semitic tribes.  Among them were the Kassi or Kossaeeans, who maintained a rude independence in their mountain fastnesses, and who, at one time, overran Babylonia and founded a dynasty there which lasted for several centuries.  The capital of Elam was Susa or Shushan, the seat of an early monarchy, whose civilisation was derived from the Babylonians.