The magnificent El-Jem amphitheatre, built in the 3C AD and the third largest in the Roman Empire (after Rome and Capua), is the best preserved monument of ancient Thysdrus. With 40 000 inhabitants during the Roman period, Thysdrus was originally a Phoenician town built at a strategic crossroads in the Sahel region. The arid landscapes surrounding El-Jem today make it hard to imagine the olive groves which once grew here and brought wealth to the city. The Romans were experts in hydraulic engineering and their skills can be admired in the tanks and pipes still visible in the amphitheatre.