In 1154, the Arab geographer Muhammad al-Idrisi created a description of the world and a world map, the Tabula Rogeriana, at the court of King Roger II of Sicily, but still Africa was only partially known to either Christians, Genoese and Venetians, or the Arab seamen, and its southern extent unknown. There were reports of great African Sahara, but the factual knowledge was limited for the Europeans to the Mediterranean coasts and little else since the Arab blockade of North Africa precluded exploration inland. Knowledge about the Atlantic African coast was fragmented and derived mainly from old Greek and Roman maps based on Carthaginian knowledge, including the time of Roman exploration of Mauritania. The Red Sea was barely known and only trade links with the Maritime republics, the Republic of Venice especially, fostered collection of accurate maritime knowledge.