TIGRIS (Old Persian Tigrd, Diklat of the cuneiform inscriptions, Hiddekel of the Old Testament, Diglath of the Targum, Digla of the Arabs) , a great river of western Asia, rising from two principal sources. The more western of these is about 10 m. S. of Lake Geuljik (Colchis of the ancients), at an altitude of 5050 ft., some 2 or 3 m. only from the channel of the Euphrates, which here forms a peninsula by a great bend (38 10' N., approximately 39 20' E.). The eastern source, which joins the main stream at Til (37 45' N., 41 46' E.), is itself divided into two branches, or rather it may be said to consist of a network of small streams, the most northerly of which has its origin in about 38 40' N. to the west of Lake Van, and close to the headwaters of the Murad Su, the eastern branch of the Euphrates, while the most easterly point is situated in a region about 42 50' E., southward of the same lake. The two sources together drain the region south as the Euphrates drains the region north of the Taurus mountains. After the junction of the two branches the river pursues a winding course, generally south-east, for about 800 m. to the point of union with the Euphrates at Garmat Ali, whence it is known as the Shatt-el-Arab until it empties into the Persian Gulf some 70 m. lower down. For some five or six centuries before 1908-1909 the junction with the Euphrates was at Korna, some 30 m. above Garmat Ali. On the western side there are no tributaries at the present day. As late as A.D. 1200, however, the Arabian geographers mention a tributary, the Tharthar, navigable in flood time, which flowed from the Jaghigagh branch of the Khabur, a tributary of the Euphrates, to the Tigris. Ormsby, in 1832, also reported a river, the Asas Amir, as coming down from the Sin jar hills and joining the Tigris near Kal-'at Shergat, about 35 30' N.; but this seems now to be a dry bed. On the eastern side of the river, on the other -Land, there are several important tributaries descending from the Persian, mountains: the Khabur, a little north of 37 N., navigable for rafts; the Great Zab, at 36 N., just below Nimrud, the ancient Calah; the Little Zab, about 35 15' N.; the 'Adhem at 34 N. and the very large and important Diyala, a little below Bagdad, at 33 15' N.
The course of the Tigris is much shorter than that of the Euphrates, about 1150 m. as compared with 1800 m., but its volume of water is greater, at least in its lower course. At Bagdad it has an average breadth of about 200 yards and a current in flood time of about 4J m. per hour. It is navigable for steamers to a point a little above the mouth of the Great Zab, about 30 m. south of Mosul, at which point navigation is blocked by two ancient dams, erected, apparently, to control the river for the Assyrian city of Calah, the ruins of which are called Nimrud by the natives after these dams, which they conceive to be the work of that mythical hero. Were it not for these dams steamers might reach Mosul itself, at an elevation of 353 ft. above the Persian Gulf. Two lines of steamers, an English and a Turkish, furnish an inadequate service between Basra and Bagdad, but there is no steam navigation on the river above the latter city. Small sailing craft navigate upwards as far as Samarra; above this all navigation is downward, and by raft. For rafts the river is navigable from Diarbekr and is termed by the natives " the cheap cameleer." The rafts used are the so-called kelleks, of wood supported on inflated skins, which are broken up at Bagdad, the wood sold and the skins carried back by caravan.
Near the source of the Tigris, at Arghana-Ma'den, are copper mines. In the neighbourhood of Diarbekr is iron. Below Mosul, for some distance, occur sulphurous and bituminous springs. There are also in that neighbourhood famous marble quarries. This part of the river's course, the ancient Assyria, is also a rich agricultural region.
From a little above the confluence of the Great Zab downward, the banks of the river are absolutely uninhabited, and the river flows through a desert until Tekrit is reached. Beginning shortly below Tekrit there are indications of considerable canalization, both for the purpose of irrigating country remote from the river, and also of shortening the course of the river for navigation. In ancient times the country on both sides of the river was well irrigated below this point, the waters of the Tigris were under thorough control, and it and its lower tributaries, the 'Adhem and the Diyala, were made, by means of huge canals, to furnish great water-ways for the country between it and the Persian hills eastward. Of these canals the best known, and probably the greatest, was the Nahrawan, which, leaving the Tigris, on its eastern side, above Samarra, over too m. north of Bagdad, rejoined it below Kut- elAmara, an equal distance to the south. None of these canals is serviceable at the present time, and few carry water in any part of their course, even in flood time.
A little south of Samarra the stony plateau of Mesopotamia ends, and the alluvial plain of Irak, ancient Babylonia, begins. Here the palm groves begin also, and from this point to a little beyond Bagdad the shores of the river are well cultivated. At the point of entering the alluvial plain the bed of the Tigris seems to be lower than that of the Euphrates, so that the canals run from the latter to the former stream. At Bagdad the Tigris and Euphrates are less than 35 m. apart, then they recede again, the Tigris bending eastward, until, below the Shatt-el-Hai, they are separated by almost 100 m. From Bagdad downward, the course of the Tigris is peculiarly serpentine and shifting. The mud brought down by it, calculated at 7150 Ib an hour at Bagdad, is not deposited in marshes to form alluvium, as in the case of the Euphrates, but although in flood time the river becomes at places an inland sea, rendering navigation extremely difficult and uncertain, the bulk of the mud is deposited in banks, shoals and islands in the bed of the river, and is finally carried out into the Persian Gulf. At Kut-el-Amara, approximately half way from Bagdad to Korna, the bed of the Tigris is higher than that of the Euphrates, and accordingly from this point downward, its waters flow into the Euphrates and not vice versa.
Shortly below Kut-el-Amara all traces of ancient canalization on the east side vanish, and it would appear as though much of that region, now largely under water at flood time, constituted an inland sea. On the west side, however, there are the remains of several canals or channels, some still carrying water, one of which, the Shattel-Hai, leaving the Tigris at Kut-el-Amara, and emptying into the Euphrates at Nasrieh, is still navigable. Indeed, in the time of the caliphate this was the channel of the Tigris, and on its banks stood the important city of Wasit. At a much more remote period also the great city of Lagash stood by or on its banks. In the time of the Sassanian kings, however, as at the present time, the Tigris occupied a more easterly course. Indeed, the lower course of the Tigris, even more than that of the Euphrates, has always been subject to change. Below the Shatt-el-Hai the country on both sides of the river is practically a swamp, except where the palm groves have formed land.
The Tigris begins to rise about the middle of November and is highest in May and June, and lowest in September and October, The principal towns on its banks are Diarbekr (anc. Amida), on the western branch; Bitlis, on the eastern branch; Mosul; Tekrit, a town dating from Persian days, said to have been founded by Shapur I. son of Ardashir I., formerly important, but now relatively insignificant; Samarra, also called Samira, the capital of the caliphate from A.D. 836 to 892, a place of pilgrimage of the Shia Moslems, containing magnificent tombs of two of their Imams the tenth and eleventh, with another much venerated shrine of the twelfth, as well as some interesting ruins; and Bagdad. While the Tigris never played the same r61e historically as the Euphrates, numerous remains of antiquity are to be seen along its course. Cuneiform inscriptions and bas-reliefs have been found at the sources of both the western and eastern Tigris, as well as at various points on the cliffs along the upper course of both branches. Opposite Mosul are the ruins of ancient Nineveh, the last capital of Assyria, and 20 m. below that the ruins of Calah, the second capital; while 35 m. farther south, on the opposite bank, lies Kal'at-Shergat, the ancient Assur, the original name-place and capital of the Assyrian Empire. A little south of Samarra are found remains of the Median Wall, which stretched south-west towards the Euphrates near Sahlawych, marking the edge of the Babylonian alluvial plain. In this neighbourhood also stood the ancient Opis. At Bagdad, besides the memorials of the caliphate, may be seen a few remains of the old Babylonian city of Bagdadu, and a dozen miles southward, on the east bank of the river, stands Takhti-Khesra, the royal palace at Ctesiphon, the most conspicuous and picturesque ruin in all Babylonia, opposite which, on the other side of the river, are the low ruin mounds of ancient Seleucia.
See W. F. Ainsworth, Researches in Assyria (1838) ; R. F. Chesney, Expedition to the Euphrates and Tigris (1850) ; W. F. Ainswortn, The Euphrates Expedition (1888); Guy Le Strange, " Description of Mesopotamia and Bagdad " (Journal of the Royal Asiatic Society, 1895) ; E. Sachau, Am Euphrat und Tigris (1900. (J. P. PE.)
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)