Ziggurats are pyramid-shaped temple mounds common to many of the early civilizations of the Near East. They probably came about from the habit of building new temples on the rubble of old ones. By 500 bc, the Persian empire stretched 4000km from India to Egypt, and had a population of over 10 million. A system of fast roads linked the capital Susa with all the outlying provinces. But the empire was weakened by frequent revolts and in 331 bc it was defeated by Alexander the Great.
Sumerian civilization begins.
Akkadians conquer Sumer. The hanging gardens built in Babylon.