Kasserine, also known as Cillium, is a city in central Tunisia with several Ancient Roman monuments and ruins.

Founded in approximately the second century AD, Kasserine became a Roman colonia known as Colonia Cillilana or just Cillium.

Just west of the main city of Kasserine, visitors can see the remains of this city, including a large ancient theatre which is carved out of the hillside, a triumphal arch and several fallen columns.

Set slightly further away from the rest of the ancient ruins, and just off the main road, is the impressive Mausoleum of the Flavii, a huge looming three-story tower-mausoleum.

Cillium is a quiet site with few people making the effort to visit the remains, particularly given the proximity of better-preserved Roman sites, such as Sbeïtla, nearby.