Chaldea, also spelled Chaldaea, Assyrian Kaldu, Babylonian Kasdu, Hebrew Kasddim, land in southern Babylonia (modern southern Iraq) frequently mentioned in the Old Testament. Strictly speaking, the name should be applied to the land bordering the head of the Persian Gulf between the Arabian desert and the Euphrates delta.
Chaldea is first mentioned in the annals of the Assyrian king Ashurnasirpal II (reigned 884/883–859 bc), though earlier documents referred to the same area as the “Sealand.” In 850 Shalmaneser III of Assyria raided Chaldea and reached the Persian Gulf, which he called the “Sea of Kaldu.” On the accession of Sargon II to the Assyrian throne (721), the Chaldean Marduk-apla-iddina II (the biblical Merodach-baladan), ruler of Bit-Yakin (a district of Chaldea), seized the Babylonian throne and, despite Assyrian opposition, held it from 721 to 710. He finally fled, however, and Bit-Yakin was placed under Assyrian control.
With this decline of Assyrian power, a native governor, Nabopolassar, was able, in 625, to become king of Babylon by popular consent and to inaugurate a Chaldean dynasty that lasted until the Persian invasion of 539 bc. The prestige of his successors, Nebuchadrezzar II (reigned 605–562) and Nabonidus (reigned 556–539), was such that “Chaldean” became synonymous with “Babylonian.”
“Chaldean” also was used by several ancient authors to denote the priests and other persons educated in the classical Babylonian literature, especially in traditions of astronomy and astrology.