The Sumerians in southern Mesopotamia are generally credited with being the earliest of ancient civilizations, followed closely by those of Egypt, China and the Indus valley. the focus of Sumerian life was the temple, the house of the god who ruled the city, the king of that time being merely his agent. In southern Mesopotamia, little stone or wood was available for building, but what did exist in huge quantity was alluvial mud, from the frequent flooding of the river. In the generally dry climate such material, which would be practically useless in more temperate regions such as northern Europe, lasts a remarkably long time, although, of course, it does not last as well as stone. The reason why the ziggurat at Ur is comparatively well preserved is that its sloping walls were carefully faced with sun-dried bricks set in mortar made from mud. An interesting feature is that the facing of the wall is interrupted at intervals by shallow vertical channels which, experts suggest, were made to allow the mud-brick core to 'breathe', preventing cracking during the wet season. The remaining lower stages have recently been restored to their original appearance.
The ziggurat was originally built by Ur-Nammu, a king of the 3rd Dynasty, during the last two centuries of the 3rd millenium BC, when Ur was the leading Mesopotamian power. It is roughly 1,000 years later than the earliest giant temples of the Sumerians such as those at Eridu and Uruk. the form of the earlier buildings - basically a monumental temple with buttressed sides raised on a huge platform - led to the ziggurat, or temple tower, which was the essential form at Ur. Ziggurats were often built on the same sites as archaic temples and have many features recalling them in form.
The great ziggurat at Ur is essentially a truncated pyramid, built in a series of platforms of diminishing area, and accessed by stairways. On the topmost platform would have been the temple of the Moon god Nanna, the chief god of Ur, although there is not trace of it now. The large temple enclosure includes royal residences and the royal tombs, which have yielded treasures of extraordinary sophistication.