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American Tract Society Bible Dictionary [1]

This name is taken, 1. For the people of Chaldea, and the subjects of that empire generally; 2. For philosophers, naturalists, or soothsayers, whose principal employment was the study of mathematics and astrology, by which they pretended to foretell the destiny of men born under certain constellations.

The Chaldeans were originally a warlike people, who at first inhabited the Carduchian or Koordish mountains north of Assyria and Mesopotamia,  Jeremiah 50:17 . As the Assyrian monarchs extended their conquests towards the north and west, the Chaldeans also came under their dominion; and this rough and energetic people appear to have assumed, under the sway of their conquerors, a new character, and to have been transformed from a rude horde into a civilized people. A very vivid and graphic description of the Chaldean warriors is given by the prophet Habakkuk, who probably lived about the time when they first made incursions into Palestine or the adjacent regions,  Habakkuk 1:6-11 . Of the date of their location in Babylonia nothing is now known. In the reign of king Hezekiah, B. C. 713, a king of Babylon is mentioned, the first of whom we read after Nimrod and Amraphel. About one hundred years later we find the Chaldeans in possession of the kingdom of Babylon. The first sovereign in the new line appearing in history was Nabopolassar. His son Nebuchadnezzar invaded Palestine, as foretold by Jeremiah and Habakkuk,  Ezra 5:12   Jeremiah 39:5 . He was succeeded by his son Evil-merodach,  2 Kings 25:27   Jeremiah 52:31 . After him came, in quick succession, Neriglissar, Laborosoarchod, and Nabonnidus or Belshazzar, under whom this empire was absorbed in the Medo-Persian. The Chaldeo-babylonian dynasty continued probably not more than one hundred years.

Smith's Bible Dictionary [2]

Chalde'ans. It appears that the Chaldeans, ( Kaldai or Kaldi ), were, in the earliest times, merely one out of many Cushite tribes inhabiting the great alluvial plain known, afterwards, as Chaldea or Babylonia. Their special seat was probably that southern portion of the country which is found to have, so late, retained the name of Chaldea.

In process of time, as the Kaldi grew in power, their name gradually prevailed over those of the other tribes inhabiting the country; and, by the era of the Jewish captivity, it had begun to be used, generally, for all the inhabitants of Babylonia.

It appears that, while both in Assyria and in later Babylonia, the Shemitic type of speech prevailed for civil purposes, the ancient Cushite dialect was retained, as a learned language for scientific and religious literature. This is no doubt the "learning" and the "tongue" to which reference is made in the book of Daniel,  Daniel 1:4.

The Chaldeans were really the learned class; they were priests, magicians or astronomers, and in the last of the three capacities, they probably effected discoveries of great importance. In later times, they seem to have degenerated into mere fortune-tellers.

Kitto's Popular Cyclopedia of Biblial Literature [3]

Chaldæ´ans is the name which is found appropriated in parts of the Old Testament to inhabitants of Babylon and subjects of the Babylonian kingdom. In 2 Kings 25, where an account is given of the siege of Jerusalem in the reign of Zedekiah, by Nebuchadnezzar the latter monarch is expressly designated 'King of Babylon' while his troops in general are spoken of as 'Chaldees,' 'the army of the Chaldees.' In , Babylon is called 'the glory of kingdoms, the beauty of the Chaldees' excellency; and in of the same book, the country is termed 'the land of the Chaldeans.' So in , 'In the first year of Darius, of the seed of the Medes, which was made king over the realm of the Chaldeans.' The origin and condition of the people who gave this name to the Babylonians, have been subjects of dispute among the learned. Probably, however, they were the same people that are described in Greek writers as having originally been an uncultivated tribe of mountaineers, placed on the Carduchian Mountains, in the neighborhood of Armenia, whom Xenophon describes as brave and fond of freedom. In the Chaldeans are spoken of in corresponding terms: 'Lo, I raise up the Chaldeans, that bitter and hasty nation, which shall march through the breadth of the land to possess the dwelling-places that are not theirs; they are terrible and dreadful; their horses are swifter than leopards and more fierce than evening wolves; their horsemen shall spread themselves; they shall fly as the eagle that hasteth to eat.' They are also mentioned in : 'Chaldeans fell upon the camels (of Job) and carried them away.' These passages show not only their warlike and predatory habits, but, especially that in Job, the early period in history at which they were known.

As in all periods of history hardy and brave tribes of mountaineers have come down into the plains and conquered their comparatively civilized and effeminate inhabitants, so these Armenian Chaldeans appear to have descended on Babylon, made themselves masters of the city and the government, and eventually founded a dominion, to which they gave their name, as well as to the inhabitants of the city and the country tributary to it, infusing at the same time young blood and fresh vigor into all the veins and members of the social frame. What length of time the changes herein implied may have taken cannot now be ascertained.

Of the kingdom of Babylon, Nimrod (, sqq.) was the founder and first sovereign. The next name of a Babylonian monarch is found in , where 'Amraphel, king of Shinar' is cursorily mentioned. A long interval occurs, till at last, in , the name of another is given: 'Berodach-baladan, the son of Baladan, king of Babylon,' it appears 'sent letters and a present unto Hezekiah; for he had heard that Hezekiah had been sick. And Hezekiah hearkened unto them, and showed them all the house of his precious things: there was nothing in his house, nor in his dominion, that Hezekiah showed them not.' On becoming acquainted with this fact, the prophet Isaiah announced that the treasures of the kingdom would be plundered and taken to Babylon along with the descendants of Hezekiah, who were to become eunuchs in the palace of the king of Babylon. The friendly act which passed between these two kings took place in the year B.C. 713. About a hundred years later, the prophets Jeremiah and Habakkuk speak of the invasion of the Chaldean army. Nebuchadnezzar now appears in the historical books, and, in , is described as 'the king of Babylon, the Chaldean, who destroyed this house (the temple), and carried the people away into Babylon.' How extensive and powerful his empire was, may be gathered from the words of —'Nebuchadnezzar, king of Babylon, and all his army, and all the kingdoms of the earth of his dominion, and all the people, fought against Jerusalem.' The result was, that the city was surrendered, and the men of war fled, together with King Zedekiah, but were overtaken in the plains of Jericho and completely routed. The Israelitish monarch was carried before Nebuchadnezzar, who ordered his eyes to be put out, after he had been compelled to witness the slaughter of his sons: he was then bound in fetters of brass and conveyed a captive to Babylon. The next Chaldee–Babylonian monarch given in the Scriptures is the son of the preceding, Evil–merodach, who () began his reign (B.C. 562) by delivering Jehoiachin, king of Judah, after the unfortunate sovereign had endured captivity, if not incarceration, for a period of more than six and thirty years. Circumstances incidentally recorded in connection with this event serve to display the magnitude and grandeur of the empire for it appears () that there were other captive kings in Babylon besides Jehoiachin, and that each one of them was indulged with the distinction of having his own throne. With Belshazzar (B.C. 538), the son of Nebuchadnezzar, closes the line of Chaldean monarchs. In the seventeenth year of his reign, this sovereign was put to death, while engaged with all his court in high revelry, by Cyrus, when he took the city of Babylon in the night season (), and established in the city and its dependencies the rule of the Medo–Persians [BELSHAZZAR].

It has been seen, from the foregoing statements, that the history of Babylon supplied by the Scriptures is brief, imperfect, and fragmentary. Little additional light can be borrowed from other quarters, in relation to the period comprised within the Biblical accounts.

Authentic history affords no information as to the time when the Chaldean immigration took place.

The kingdom of the Chaldees is found among the four 'thrones' spoken of by Daniel (, sqq.), and is set forth under the symbol of 'a lion having eagles' wings. The government was despotic, and the will of the monarch, who bore the title of 'King of Kings' (), was supreme law, as may be seen in ; . The kings lived inaccessible to their subjects in a well-guarded palace. The number of court and state servants was not small; in , Darius is said to have set over the whole kingdom no fewer than 'an hundred and twenty princes.' The chief officers appear to have been a sort of 'mayor of the palace,' or prime minister, to which high office Daniel was appointed (), 'a master of the eunuchs' (), 'a captain of the king's guard' (), and 'a master of the magicians,' or president of the Magi (). Distinct probably from the foregoing was the class termed (; ) 'the king's counselors,' who seem to have formed a kind of 'privy council' or even 'cabinet' for advising the monarch and governing the kingdom. The entire empire was divided into several provinces (; ), presided over by officers of various ranks. An enumeration of several kinds may be found in . The head officers, who united in themselves the highest civil and military power, were denominated 'presidents' (); those who presided over single provinces or districts bore the title of 'governor.' The administration of criminal justice was rigorous and cruel, will being substituted for law, and human life and human suffering being totally disregarded. Nebuchadnezzar () declares to the college of the Magi—'If ye will not make known unto me the dream with the interpretation thereof, ye shall be cut in pieces, and your houses shall be made a dunghill' (see also ; ; ). The religion of the Chaldees was, as with the ancient Arabians and Syrians, the worship of the heavenly bodies; the planets Jupiter, Mercury, and Venus were honored as Bel, Nebo, and Meni, besides Saturn and Mars. Astrology was naturally connected with this worship of the stars, and the astronomical observations which have made the Chaldean name famous were thereby guided and advanced. The language spoken in Babylon was what is designated Chaldee, which is Shemitic in its origin, belonging to the Aramaic branch. The immigrating Chaldeans spoke probably a quite different tongue, which the geographical position of their native country shows to have belonged to the Medo–Persian stock.

The term Chaldeans represents also a branch of the order of Babylonian Magi. In they appear among 'the magicians, and the astrologers, and the sorcerers,' who were 'called for to shew the king his dream.' In they are represented as speaking in the name of the rest; or otherwise theirs was a general designation which comprised the entire class (; ): a general description of these different orders is found in , as 'the king's wise men.'