Today the term "Chaldean" is used to refer to a branch of the Nestorian Orthodox church that became affiliated with Rome while preserving its liturgical language and ecclesiastical customs. For example, Chaldean priests, unlike their counterparts in the Roman church, are allowed to marry. Chaldeans number at present about 200,000 Nestorian Catholics and 75,000 Jacobite Catholics, who are sometimes confused with Chaldeans. In 1646 Jacobites who were drawn to Catholicism were termed "Syrian Uniates" instead of "Chaldeans." "Uniat(e)" refers to all Eastern-rite churches that affiliated with Rome, including that of the Chaldeans. The Jacobites were part of the Chaldean church until they went their separate way.
The term "Chaldeans" was originally a designation for the inhabitants of Babylon in the first millennium B . C . First Greek and Roman writers—and, later, Alexander the Great—employed the term to refer to these people, who had invented astrology and had strongly influenced Roman writers and the leading thinkers of the East and West in postulating that astrology could ascertain the will of the gods and human destiny. The Church Fathers attacked the Chaldeans repeatedly and strongly because they believed that such theories would mitigate their own notions of how to determine the will of the one God. The earliest mention of Chaldeans occurs in the Bible, in reference to Nebuchadnezzar destroying Assyria, then conquering Syria and Palestine in 597 B . C ., which events were followed by the so-called Babylonian Captivity of Hebrew notables. The latter were freed in 539 B . C . by the Persian king, Cyrus, who ended Chaldean primacy in the whole region.
The Uniates have nine Eastern patriarchs. Those of Constantinople, Alexandria, and Antioch live in Rome. In addition there are Uniate patriarchs of Jerusalem (Greek), Antioch (Syrian and Maronite), and Babylon (Chaldean). The Syrian Uniates use the liturgy of St. James, write in Karshūni (Arabic in Syriac script), and conduct prayers in both Syriac and Karshūni (inaudibly in Syriac). The Chaldean Uniates, on the other hand, use the liturgy of Addai and Mari, which was first adopted by the Nestorians (but in a much abridged form in its daily application, when compared to the original that is still employed by the Nestorians). Like the Maronites, they are sometimes referred to as Eastern Uniates (i.e., Eastern-rite Christians who acknowledge the primacy of the pope in Rome). The Chaldeans use one of the eighteen canonical rites that are recognized by the Holy See. They reside today in Iran, Iraq, Syria, Lebanon, and Turkey, subject to the Chaldean patriarch of Babylon. They are for the most part descended from the East Syrian or ancient Aramaean and Babylonian peoples who were Christianized when Persia ruled the East. The Persians accepted the so-called heresy of the Nestorians, and the Muslim Arabs who replaced them have allowed the Eastern Christian churches to continue to employ their rites under the protective umbrella of Islam. Each church member bears the officially recognized status of dhimmi (i.e., a non-Muslim permitted to retain his or her original faith).