<P> 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 on the coast since 1445, and trade with the wealthier Europeans became of prime importance to West Africa . North Africa had declined in both political and economic importance, while the Saharan crossing remained long and treacherous . However, the major blow to trans - Saharan trade was the Battle of Tondibi of 1591--92 . Morocco sent troops across the Sahara and attacked Timbuktu, Gao and some other important trading centres, destroying buildings and property and exiling prominent citizens . This disruption to trade led to a dramatic decline in the importance of these cities and the resulting animosity reduced trade considerably . </P> <P> Although much reduced, trans - Saharan trade continued . But trade routes to the West African coast became increasingly easy, particularly after the French invasion of the Sahel in the 1890s and subsequent construction of railways to the interior . A railway line from Dakar to Algiers via the Niger bend was planned but never constructed . With the independence of nations in the region in the 1960s, the north--south routes were severed by national boundaries . National governments were hostile to Tuareg nationalism and so made few efforts to maintain or support trans - Saharan trade, and the Tuareg Rebellion of the 1990s and Algerian Civil War further disrupted routes, with many roads closed . </P> <P> Traditional caravan routes are largely void of camels, but the shorter Azalai routes from Agadez to Bilma and Timbuktu to Taoudenni are still regularly--if lightly--used . Some members of the Tuareg still use the traditional trade routes, often traveling 2,400 km (1,500 mi) and six months out of every year by camel across the Sahara trading in salt carried from the desert interior to communities on the desert edges . </P> <P> The African Union and African Development Bank support the Trans - Sahara Highway from Algiers to Lagos via Tamanrasset which aims to stimulate trans - Saharan trade . The route is paved except for a 200 km section in northern Niger, but border restrictions still hamper traffic . Only a few trucks carry trans - Saharan trade, particularly fuel and salt . Three other highways across the Sahara are proposed: for further details see Trans - African Highways . Building the highways is difficult because of sandstorms </P>

When did the gold and salt trade start