The Subtropical Southwest. This consists of the peninsula of Arabia, an old crustal block which forms a worn tableland with its surface generally tilted down towards the east. As in the Deccan, the western edge stands up as a mountain ridge. Its shores are washed by the Red Sea whose waters fill the depression formed by the northern portion of the Great Rift Valley of Africa. The line of sinking is continued, though in smaller proportions, through the Gulf of Aqaba, the Dead Sea, and the Jordan valley up to and beyond the Sea of Galilee.

The position of Arabia within the high-pressure belt of the Tropic of Cancer and in the midst of the three great land masses of Asia, Africa, and Europe makes the peninsula into a barren region. Only in the extreme southwest in Yemen, the old Arabia Felix of the Romans, and in the east in Oman, does sufficient rain fall to support more than a sparse, xerophilous vegetation. In the Hadhramaut, or southeast coast strip, the hollows between the broken, rocky hills are sand-filled, with extensive thickets of acacia and tamarisk. In the centre the Nejd has a similar, though far sparser, vegetation, and along the Red Sea coast palms grow and cultivation is possible in small areas. But the Nefud Desert in the north and the Great Arabian Desert of the south are unredeemed stretches of bare sand and rock, with an occasional oasis.

The population is therefore small and widely scattered. Little towns occur along the west coast and on one or two of the larger oases, and in these a more or less settled population feeds itself by cultivating millet in irrigated fields. Mecca and Medina are the headquarters of Islam and are visited annually by large numbers of pilgrims, on the supply of whose wants the town populations live. The Hejaz railway, which formerly connected Medina with Damascus, has been allowed to fall into disuse. Away from the towns the people are nomads, passing from oasis to oasis in patriarchal bands which carry on petty wars with each other and often attack the settled townsfolk. The only economic product which enters world trade is a small amount of the famous mocha coffee, so named after the town from which it is exported.