The Central African mountains not only cover extensive areas, but by reason of their latitude they belong definitely to the true equatorial zone. Consequently great quantities of tropical rains are brought to the Sahara by such rivers as the Niger, the Shari, which ends in Lake Chad, and especially the Nile. There is hardly any need to emphasize the fact that life in the Sahara is dependent on its resources of water, and that in consequence the existing rivers are of primary importance. The Niger is a Saharan river by reason of its loop, on which Timbuktu is situated. Rising in the mountains of Futa-Jallon on the coast of the Gulf of Guinea, it first turns its back on this gulf and flows straight north as far as the Saharan zone. The Shari is almost an exact counterpart of the Niger, except that it terminates in Lake Chad.