The Chaldeans and Medes united to overthrow Nineveh in 612 BCE, leading to the division of the Assyrian Empire and the establishment of a Chaldean empire in Mesopotamia. Key contributions of the Chaldeans include advancements in mathematics and astronomy, as well as the construction of Babylon by Nebuchadnezzar II, a symbol of their power. However, this empire fell to the invading Persians in 539 BCE.