El Djem is a town in Mahdia Governorate, Tunisia, population 18,302. It is home to some of the most impressive Roman remains in Africa. The city was built, like almost all Roman settlements in Tunisia, on former Punic settlements. In a less arid climate than today's, Roman Thysdrus prospered especially in the 2nd century, when it became an important center of olive oil manufacturing for export. It was the seat of a Christian bishop - which is still occupied by a titular Roman Catholic bishop today.