The port of Algiers is sheltered from all winds. There are two harbours, both artificial—the old or northern harbour and the southern or Agha harbour. The northern harbour covers an area of . An opening in the south jetty affords an entrance into Agha harbour, constructed in Agha Bay. Agha harbour has also an independent entrance on its southern side. The inner harbour was begun in 1518 by Khair-ad-Din Barbarossa (see History, below), who, to accommodated his pirate vessels, caused the island on which was Fort Penon to be connected with the mainland by a mole. The lighthouse which occupies the site of Fort Penon was built in 1544.