This massive fortified gate, one of Tunisia’s finest, is all that survives of the original Fatimid city. Entry is through a narrow, vaulted passageway, almost 50m long, that was once protected by a series of gates – one of them a suitably oversized iron portcullis. On market day, the interior is lined with impromptu stalls; it’s just possible to imagine you’re entering an ancient town little changed in centuries.
You can also climb to the top from the Musée de Mahdia (paid entry).