A. The Sumerians only knew of five planets, not 12.
B. True, Sumer was a site of innovative primary urbanization, but cities had been builing walls for centuries before them, and the only real innovation they had was a written language, which changed slowly from tally marks for merchants to the complex priestly records and legends. Their calandar was not very accurate (360 days) and required constant adjustments to keep the seasons in line.
C. The Sumerians did not advance quickly, but stayed at nearly the same technological level for the 1000 or so years of their existance - only advancing after they were conquered by the Akkadians and brought into the Akkadian Empire.
D. The Ziggurats were easily constructed compared to the pyramids, requiring around 10,000 people working 80 days a year (between planting and harvest) for 15-18 years.
E. "The Epic of Gilgamesh" kicks ass! Read it!
Chris