Sumer was in fact a city-state, so the main city was Sumer itself
In ancient Sumer and Babylonia, most structures were made of Mud Brick. you are welcome!
The Sumerians obtained most of their wealth and success from trade.
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Most scholars designate around 3500-3100 BCE as the beginning of the first true civilization in Sumer. This period marks the emergence of city-states, writing systems (such as cuneiform), advanced architectural developments like ziggurats, and complex societal structures in the region.
Sumer covers only the southern part of Mesopotamia, so Babylon (probably) and Nineveh (certainly) should be excluded. The then most prominent cities were Ur, Eridu, Bad-tibira, Larsa, Sippar and Shuruppak.
The majority of the river civilizations of the ancient times had a King or an Emperor from the Sumer to Assyrian right through the Achaemenide Persian Empire.
Prior to the introduction of Buddhism, the most prominent religion of China was Taoism.
Athens and Sparta were the two most powerful city-states in ancient Rome.
Certainly Charleston must be the most prominent city for the arts in that state.
The most famous and powerful of all the city states of ancient Greece were Sparta and Athens.