The Sumerians were conquered by the Mesopotamians, who were conquered by the Assyrians, who were conquered by the Persians.

The society was not under one ruler ship, but made up of city centered social collectives that worked together for common good and this type of structure remained.

The temple was the centre of the city and shops, businesses and dwellings radiated out from it. 

As lofty heights were seen as being the only places fit for the inhabitance of the gods, the Sumerians built elevated temples called ziggurats.

The first ziggurat was the 'White Temple' (whitewashed walls) and preceded the first such Egyptian structure by several centuries.

Ziggurats reached the size of man made mountains and included towers. One of these towers was the famous tower of Babylon. It was in these that the gods were assumed to dwell.

During this time, the art and architecture retained a continuity, primarily because all of these different tribes came from the surrounding territory and were held together with common beliefs and ancestry.

You will see, in spite of the separation of the culture, a similarity of the architecture to the Egyptians.

Much less remains of the buildings from this time as the materials used to construct the buildings were not of the same hard stone as the Egyptians, and so much has eroded over time.