TIGRI. - One of the two great rivers—the eastern one—that flow from the eastern borders of Asia Minor in a south-easterly direction as far as the Persian Gulf, forming the “valley of the two rivers” (Mesopotamia [v.]), one of the regions that witnessed the dawn of human civilization.
In its upper course the river, formed by 4 main branches descending into the southern valleys of the Armenian mountain system (west and south of Lake Van), waters several centres, such as Amida and Maṭarah. The river thus formed flows southward, with a slight inclination eastward, receiving many tributaries descending from the Zagros range, such as the Greater and Lesser Zāb (Zābāc), the 'Adēm (Radānu, Φάσος), and the Djālah (Turnat, Tornadotus). Along its middle course stand some of the greatest centres of antiquity: Nineveh, Kalab (Nimrūd), Assur (Qal'at Šerqāt). At the level of present-day Bagdad the T. comes remarkably close to the Euphrates (about 50 km.), then, moving slightly away from it, formerly reached the sea through its own outlet; in this stretch too it waters important centres, such as Upi ('Oruç) and Kūt el-'Amārah. Today, however, before reaching the sea, the T. joins the Euphrates, forming the Šaṭṭ el-'Arab, which flows for 50 km. through a stretch of alluvial plain where the sea once lay.
In the Bible the T. (Hebr. Hiddegel; Sumerian Idigna, Akkadian Idiglat, Diglat; Aram. Dighlath, Arabic Diglah; in Old Persian the Aramaic name became phonetically Tigrā, whence the Greek-Latin Tīyquc) is recalled as one of the four rivers of Paradise (Gen. 2,14), and as the river of Mesopotamia it is mentioned in the later historical books (Dan. 10,4; Tob. 6,1; Iudt. 1,6; Eccli. 24,35 [25]).