The original 9th-century walls enclosing this fortified Arab city were bulked out into a Crusader fortress by King Louis IX of France (St Louis), better known for building Ste-Chapelle in Paris. The ramparts, 900m long and 13m high, were made all the more impassable by a 9m-deep moat. To get an overview of the site, head up the slope from the minaret by the harbour.
A path leads to the remains (three rounded apses) of a 13th-century Crusader Church, built over the site of an older Byzantine church.
The ruined city, situated between the national park's northern entrance and the harbour, is accessible whenever the park is open.