Ancient region, on the headwaters of the Euphrates River and adjacent to the Persian Gulf .
It was originally the southern part of Babylonia ; the name Chaldea also has been used (especially in the Bible) to describe all of Babylonia after it was occupied by the Chaldeans, who established a Chaldean (or neo-Babylonian) dynasty с 625 BC. Under Nebuchadrezzar II , the empire expanded, subduing Judaea and capturing Jerusalem . It fell to the Persian Achaemenian dynasty in 539 BC.