El Djem or El Jem is a town in Mahdia Governorate, Tunisia. Its population was 21,544 at the 2014 census. It is home to Roman remains, includi…El Djem or El Jem is a town in Mahdia Governorate, Tunisia. Its population was 21,544 at the 2014 census. It is home to Roman remains, including the Amphitheatre of El Jem. The Roman city of Thysdrus was built, like almost all Roman settlements in ancient Tunisia, on former Punic settlements. In a less arid climate than today's, Thysdrus prospered as an important center of olive oil production and export. It was the seat of a Christian bishopric, which is included in the Catholic Church's list of titular sees.