TIGRIS. - One of the two great rivers - the eastern one - that flow from the eastern borders of Asia Minor in a south-easterly direction to 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 that descend into the southern valleys of the Armenian mountain system (to the west and south of Lake Van), bathes several centers, such as Amida and Maṭarah. The river thus formed flows southward, with a slight inclination to the east, receiving many tributaries that descend from the Zagros range, such as the Great and Little Zāb (Zābāc), the 'Adēm (Radānu, Φάσος), the Djālah (Turnat, Tornadotus). On its middle course rise some of the greatest centers of antiquity: Nineveh, Kalab (Nimrūd), Assur (Qal'at Šerqāt). At the height of present-day Baghdad the T. comes notably close to the Euphrates (ca. 50 km.), then, gradually drawing away from it, in ancient times it reached the sea by an outlet of its own; also along this stretch it bathes important centers, such as Upi ('Oruç) and Kūt el-'Amārah. Today, however, before its outlet to the sea the T. joins with the Euphrates, forming the Šaṭṭ el-'Arab, which flows for 50 km. through a stretch of alluvial plain where the sea once was.
In the Bible the T. (Heb. Hiddegel; Sum. Idigna, Akkadian Idiglat, Diglat; Aramaic Dighlath, Arabic Diglah; in Old Persian the Aramaic name phonetically became Tigrā, whence the Greco-Latin Tīyquc) is remembered as one of the four rivers of Paradise (Gen. 2:14) and as a river of Mesopotamia it is mentioned in the later histories (Dan. 10:4; Tob. 6:1; Jdt. 1:6; Sir. 24:35 [25]).
Giovanni Rinaldi