El Djem (Arabic: قصر الجمّ; Latin Thysdrus) is a town in Mahdia Governorate, Tunisia, population 18,302 (2004 census). 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.

By the early 3rd century AD, when the amphitheater was built, Thysdrus rivaled Hadrumetum (modern Sousse) as the second city of Roman North Africa, after Carthage. However, following the abortive revolt that began there in 238 AD, and Gordian I's suicide in his villa near Carthage, Roman troops loyal to the Emperor Maximinus Thrax destroyed the city. It never really recovered.

The amphitheater was used for filming some of the scenes from the 1979 Monty Python film The Life of Brian and was also used for filming some of the scenes from the Academy Award (Oscar) winning film Gladiator starring Russell Crowe as a leading actor. The main scenes were actually filmed in Fort Ricasoli on Malta.