The whole of North Africa is covered by a great desert, bordered only on the northwest by a considerable arable district, which at present forms the states of Morocco, Algiers, and Tunis. Except for this, if we set aside a single strip of coast land in the country between the two Syrtes (Tripolis, Leptis) and in Cyrenaica (Bengari), this whole territory is totally destitute of all higher civilisation. It forms the natural frontier of the Mediterranean world, beyond which not even ancient civilisation ever penetrated. The interior of Africa was practically unknown to the Greek and Roman world. The formidable desert land, embracing more than three million square miles, contains a series of depressed levels in which springs are harboured, and vegetation, especially the date-palm, thrives. These are the oases. Here, and here only, are permanent human settlements possible. At the same time the oases form stations in the wearisome and difficult way through the desert, where the trader who wants to acquire goods in the countries on the other side is exposed not only to the dangers that threaten him from want of water, loss of his way, and sand-storms, but also to the attacks of vagrant robber hordes that traverse the desert in nomadic confusion. East of the great desert, at a distance of a few days’ journey from the Arabian Gulf, lies a straggling fruitful valley, which in some sense may be regarded as an oasis of colossal dimensions. This is Egypt, the valley of the Lower Nile. On both sides it is bounded by desert land. On the west rises the plateau of the Libyan Desert, flat, absolutely barren, covered with impenetrable sand-banks. On the east a rocky highland of solid quartz and chalk rises in a gradual slope, at the back of which the crystalline masses of the so-called Arabian Mountains ascend to a height of about six thousand feet. In geological structure the two territorial districts are entirely different, but, although it is true that nomadic hordes can, at a pinch, keep body and soul together in the eastern desert, and that they are not entirely cut off from vegetation, from springs and cisterns in which the rainwater is gathered up from storm and tempest, civilisation is as much sealed to them as it is to the Libyan waste, through which it is impossible to penetrate, and which is habitable only in the oases.