The first use of a cannon as a siege engine is now thought to be in 1274 at the siege of Sijilmasa, the medieval city on the northern edge of the Sahara Desert in Morocco. Being a trading centre, it was one of the most economically important cities of the Maghreb, described in medieval Arab texts as the City of Gold. In the 14th century Arab historian Ibn Khaldun's account of how the Marined Sultan of Morocco, Abu Yusuf, successfully laid siege to the city, he stated that the cannon discharged small pieces of iron by means of ???arud?? a burning powder, presumed to be a form of gunpowder.