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.
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.
Sala-ud-din, " Honouring the Faith") (1138-1193), first Ayyubite sultan of Egypt, was born at Tekrit in 1138.
Bicolor); lentils, peas, beans, vetches; cotton, hemp, safflower, tobacco; Medicago sativa (for horses); cucumber, melons, water-melons, figs (those of Sinjar famed for sweetness), dates (below, 'Ana and Tekrit); a few timber trees; plane and white poplar (by streams), willow and sumach (by the Euphrates).
Id), on the Euphrates; Jeziret ibn `Omar, Mosul (q.v.), Tekrit, on the Tigris; Edessa (q.v.), Harran (q.v.), on confluents of the Belikh; Veranshehr (Tela), Ras al-`Ain (Rhesaena), Mardin (half-way up the mountain wall), and Nasibin (Assyr.
The Arab tribes in Mesopotamia were Christian, and Heraclius at Edessa hoped for their support; but Karkisiya and Hit succumbed (636), and then Tekrit; and Heraclius retired to Samosata.
To the same period belong other Atabeg dynasties; Begtiginids at Harran, Tekrit, &c.; Ortokids at Edessa, 'Ana, &c., with Mardin as their headquarters.
At the present time it extends from a point just below Kut el-Amara to a point somewhat above Tekrit on the Tigris, and from a point somewhat below Samawa to a point a little above Anah on the Euphrates.
Between the Euphrates and the Arabian plateau lie the sacred cities of Kerbela or Meshed-Hosain, and Nejef or Meshed Ali, with a population of 20,000 to 60,000 each, while a number of towns, varying in population from 3000 to 10,000, are found along the Euphrates (Anah, Hit, Ramadieh, Musseyib, Hilla, Diwanieh and Samawa) and the Tigris (Tekrit, Samarra and Kut elAmara).