TIARET (Tahert), a town of Algeria, in the Tell Atlas, department of Oran, 122 m. S.E. of Mostaganem by rail. It occupies an important strategic position on a pass through the mountains at an elevation of 3552 ft. Pop. (1906), 5778, of whom 3433 were Europeans. The Wadi Tiaret flows through the town in a series of cascades. The upper town, the residential quarter, is on the right bank of this stream. The citadel occupies a separate hill on the other side of the wadi. The chief business centre is the lower town where are also the principal public buildings. On another hill opposite the citadel is the native town.

The citadel occupies the site of a Roman station believed to be that of Tingurtia. Tiaret (Berber for “station ”) was a town of note at the time of the Arab invasion of North Africa in the 7th century and is stated by Ibn Khaldun to have offered a stubborn resistance to Sidi-Okba. In 761 it was taken by Abdurrahman ibn Rostem, the founder of the dynasty of the Beni Rustām (Rostem). Their empire, which during the reign of Abdurrahman (761-784) and his son Abdul Wahab (784-823) extended over the greater part of the modern Algeria, was known as the Ibadite Empire from Abdallah ibn Ibad, the founder of the heretical sect to which Abdurrahman belonged. The Ibadites represented the moderate section of the Kharijites (see Mahommedan Religion). Seven princes of the Rustamite house succeeded Abdul Wahab at Tiaret, but in 909 the dynasty was overthrown by the Fatimite general al Shi'i. Two years later Tiaret was captured by Massala ibn Habbus of the Miknasa dynasty of Morocco, and after his death in 924 two other princes of the same house maintained their independence, but in 933 the Fatimites again gained the mastery. The Ibadites, after being expelled from the Tell, took refuge in Wargla. They were driven thence in the 11th century and migrated to Mzab, where their descendants still profess the Ibadite doctrines (see Mzabites). After its second capture by the Fatimites, Tiaret ceased to be the capital of a separate state. For a long period it was included in the sultanate of Tlemçen, and in the 16th century fell to the Turks. It was one of the chief towns of Abd el Kader, but was occupied by the French in 1843. At Takdempt, 6 m. west of Tiaret, Abd el Kader had his principal arsenal. About a mile from Takdempt are ruins of a town supposed to be the remains of the Ibadite capital. Eighteen miles S.S.W. of Tiaret are the sepulchral monuments known as the Jedars (see Algeria: § Archaeology).