Coordinates: 35°10′N 8°50′E / 35.167°N 8.833°E / 35.167; 8.833
Kasserine (Arabic: ڨصرين Gaṣrīn) is the capital city of the Kasserine Governorate, in west-central Tunisia. It is situated below Jebel ech Chambi, Tunisia's highest mountain. Its population is 76,243 (2004).
In classical antiquity it was a Roman colony, known as Cillium. Under Roman Emperor Vespasian (69-79) or Titus (79-81), it was elevated to the rank of municipium, and under the Severan dynasty to that of colonia (Cillilana). Archaeological evidence remains on site: mausoleums, triumphal arches, thermae, a theatre and a Christian basilica.
Cillium was important enough in the Roman province of Byzacena to become a suffragan of the Metropolitan of Hadrumetum.
In 411, Cillium was represented at the Conference of Carthage between Catholic and Donatist bishops by the Catholic Tertiolus and the Donatist Donatus. In 484, Fortunatianus of Cillium was one of the Catholic bishops whom the Arian Vandal king Huneric summoned to Carthage and then exiled.