They destroyed the Kassite in Akkad and Sumer. Soon after the construction of the new Assyrian capital, Nineveh. It was very beautiful with a library and a zoo. The water supply was poor. The Assyrians were very hated. The Medes took control of Assyria in 612 BCE and invaded Anatolia. The Chaldeans (New Babylonians) became the new masters of Mesopotamia. Their greatest cultural achievements were in astronomy. They studied the sky because they believed gods lived there. The Persian Empire was ruled by Darius the Great from 522 to 485 BCE. He spent years improving the administrative organization, then worked to expand the empire. This empire lasted longer than all others because people could follow their own laws as long as they paid their taxes. The Persian army also provided better protection against invasions. They used a cuneiform script borrowed from the Summerians. The most unifying forces they used were the Universal System of Weights and Measures, the road system, the postal service and Zoroastrianism which was based on individual principles.