TIARET (Tahert), a town of Algeria, in the Tell Atlas, de partment of Oran, 122 m. S.E. of Mostaganem by rail. It occu pies an important strategic position on a pass through the moun tains at an elevation of 3,552 ft. 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 railway, which ended there and which has been extended to Trumelet, forms the outlet of the fertile Sersou plateau, the 400,000 hectares of which have been completely transformed by colonization since 190o.
The citadel occupies the site of a Roman station. Tiaret (Berber for "station") was a town of note at the time of the Arab invasion of North Africa in the 7th century. In 761 it was taken by Abdurrahman ibn Rostem, the founder of the dynasty of the Beni Rustam (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 ISLAM.) Seven princes of the Rustamite house succeeded Abdul Wahab at Tiaret, but in 909 the dynasty was overthrown by the Fatimites. The Ibadites, after being expelled from the Tell, took refuge in Wargla. They were driven thence in the II th century and migrated to Mzab, where their descendants still pro fess the Ibadite doctrines and traditions. After its second cap ture by the Fatimites, Tiaret ceased to be the capital of a separate state. For a long period it was included in the sultanate of Tlemcen, and in the i6th century fell to the Turks. It was one of the chief towns of Abd el Kader, but was occupied by the French in 1843. (See ALGERIA.)