The Sahara desert effectually divides Africa in two. The northern coast shared in the classical and medieval history of the Mediterranean and does not concern us here. Sub-Saharan Africa, how-ever, is far from uniform geographically. The Congo rain Forest is bordered north, east, and south by savanna-that is, landscapes of grass dotted by occasional clumps of trees. But the mountains and great lakes of central east Africa interrupt the arc of the savanna, so that it is not a continuous belt, but divides into two major parts: west Africa, bisected by the curved course of the Niger river, and east Africa, running down the east spine of the continent all the way to the Cape of Good Hope. Scant pasture lands, fringing the southern Sahara, skirt the northern face of the mountain barrier. This miniature steppe therefore linked the two major productive regions of east and west Africa.