trade. Northern economies were short of gold but at times controlled salt mines such as Taghaza in the Sahara, whereas West African countries like Wangara had plenty of gold but needed salt. Taghaza, a trading and mining outpost where Ibn Battuta recorded the buildings were made of salt, rose to preeminence in the salt trade under the hegemony of the Almoravid Empire. The salt was mined by slaves and purchased with manufactured goods from Sijilmasa. Miners cut thin rectangular slabs of salt directly out of the desert floor, and caravan merchants transported them south, charging a transportation fee of almost 80% of the salt's value. The salt was traded at the market of Timbuktu almost weight for weight with gold. The gold, in the form of bricks, bars, blank coins, and gold dust went to Sijilmasa, from which it went out to Mediterranean ports and in which it was struck into Almoravid dinars. Spread of Islam The spread of Islam to sub-Saharan African was linked to trans-Saharan trade. Islam spread via trade routes, and Africans converting to Islam increased trade and commerce. Historians give many reasons for the spread of Islam facilitating trade. Islam established common values and rules upon which trade was conducted. It created a network of believers who trust each other and therefore trade with each other even if they do not personally know each other. Such trade networks existed before Islam but on a much smaller scale. The spread of Islam increased the number of nodes in the network and decreased its vulnerability. The use of Arabic as a common language of trade and the increase of literacy through Qur'anic schools, also facilitated commerce. Muslim merchants conducting commerce also gradually spread Islam along their trade network. Social interactions with Muslim merchants led many Africans to convert to Islam, and many merchants married local women and raised their children as Muslim. Islam spread into Western Sudan by the end of the 10th century, into Chad by the 11th century, and into Hausa lands in 12th and 13th centuries. By 1200, many ruling elites in Western Africa had converted to Islam, and from 1200 to 1500 saw a significant conversion to Islam in Africa. Decline of trans-Saharan trade The Portuguese journeys around the West African coast opened up new avenues for trade between Europe and West Africa. By the early 16th century, European trading bases, the factories established