It is surprising that at the close of the nineteenth century there should remain so many portions of our globe still unexplored. We have better maps of the north pole and of the moon than we have of Southeastern Arabia and parts of Central Asia. A triangle formed by lines drawn from Harrara in Oman to El Harik in Southern Nejd, thence to Marib in Yemen and back to Harrara will measure very nearly 500 miles on each of its upper sides and 800 on the base. This triangle, with an area of 120,000 square miles is as utterly unknown to the world at large as if it were an undiscovered continent in some polar sea. Never has it been crossed by any European traveller or entered by an explorer. It includes all the _hinterland_ of the Mahrah and Gharah tribes, all western Oman and the so-called Roba’-el-Khali (literally, “empty abode”) of the Dahna desert, as well as that mysterious region of El Ahkaf to which the Koran refers and which is said by the Arabs to be a sea of quicksands, able to swallow whole caravans. On most maps the region in question is left blank; others designate it as an uninterrupted desert from Mecca to Oman; while Ptolemy’s map describes the region as producing myrrh and abounding in Arab tribes and caravan-routes. Whatever we know of the country at present must be the result of Arab hearsay booked by travellers in the coast-provinces. The few names of places given in the Roba’-el-Khali would _not_ lead one to suppose that “uninterrupted desert” was its only characteristic feature. In the north are Jebel Athal (the Tamarisk Mountains), and Wady Yebrin. Wady Shibwan and Wady Habuna seem to extend at least some distance into the triangle from the west, while, in the very centre we have the very unusual names for a desert region Belad-ez-Zohur (Flower-country) and El-Joz (the nut-trees). There is no doubt that a large part of the region is now desert and uninhabited; but it may not always have been so and may hold its own secrets, archæological and geographical.