Coming to Monastir from almost any other part of Tunisia, you will be surprised to discover how densely populated the small triangle just south of Sousse is. There's a burgeoning town every few kilometres. Originally built as a trading post by the Phoenicians and then by the Romans under the name of Ruspina, Monastir became important once again in the eighth century with the establishment of its fortified Ribat. The Ribat has the appearance of an imposing monastery, and was intended as a defence against sea-faring invaders. It houses an Islamic museum, and in summer son et lumiere presentations light up its walls.