Borj El Kebir, also known as Borj Ghazi Mustapha, is the largest and best-preserved fortress on Djerba island, located in Houmt El Souk near the fishing port. It was built in the end of the 14th century over the ruins of the ancient Roman city of Griba, after the deportation of the soldiers of Alfonso V of Aragon on the orders of the Hafsid sultan of Tunisia, and was later extended in 1450. The name Borj El Ghazi Mustapha comes from the Qaid who settled in Djerba in 1559. In 1903, it became a property of the Tunisian authorities who gave it the status of a national historical monument on 15 March 1904 and transformed it into a museum. Restoration started in 1969 and was completed by the early 1980s. The borj has a rectangular form. Nowadays, the monument has two mausoleums: Sidi Saad, and Ghazi Mustapha, for Ghazi Mustapha Bey. Today, it remains one of the most visited historical sites on the island.