The Sahara is not everywhere an utter desert; there are many oases—trenched valleys with wells to the water percolating underground in their bottoms, or hilly tracts against which at times the clouds gather—but these are minute and scattered exceptions upon a barren and riverless area nearly as large as all Europe. The Sahara is the most unbroken natural boundary in the world; throughout History it has been a barrier between the White and the Black men.
Between the Sahara and the Heartland there is a broad gap which is occupied by Arabia. The two brinks of the Nile Valley are known as Libyan to the West and Arabian to the East; and away beyond the Lower Euphrates, at the foot of the Persian Mountains, is the district known as Arabistan or the country of the Arabs. In complete harmony, therefore, with local usage, Arabia may be regarded as spreading for 800 miles from the Nile to beyond the Euphrates. From the foot of the Taurus Mountains, north of Aleppo, to the Gulf of Aden, it measures no less than 1800 miles. As to one-half, Arabia is desert, and as to the other half mainly dry steppes; although it lies in the same latitudes as the Sahara, it is more productive and carries a more considerable population of
