The Yemen may be described as forming the south-west corner of Arabia. So little is known of the geography of the interior, and to such a slight extent do even the natives define the boundaries between their own land and the surrounding provinces, that any exact description of the country is impossible. The same may be said of nearly all oriental frontiers, except where, taking an example from European customs, a clear line of demarcation has been agreed upon; for, as a rule, limits depend far more upon tribal position and inheritance than upon any natural features of the land in question; and in many cases in the settlement of frontier questions with oriental Powers, even European Governments have been obliged to follow upon these lines. This is especially clearly exemplified in the case of the Algerian and Moroccan frontier, in the southern parts of which no absolute boundary has been fixed, certain tribes, whether in French or Moorish territory, belonging to whichever of the two nationalities under which they are enrolled. How infinitely difficult it is, then, in the case of the Yemen, to state where that province begins and ends, will be appreciated. As to two of its limits, the task of definition is simple; for on the west the Red Sea, and on the south that portion of the Indian Ocean known as the Gulf of Aden, allow of no question. On the north and east far more serious difficulties arise. Without attempting to delineate any exact frontier, which, with our present geographical knowledge of the country, would fail at the best to be anything more than roughly correct, more general terms must be used than would be justifiable in a more pretentious work than the present. It may be stated, then, that the province of Arabia known as the Yemen is bounded on the east by the Hadramaut tribes, and on the north by the Asir, although some authorities include the latter, making the north frontier of the Yemen adjacent with the southern limit of the Hejaz, the province of Arabia in which are situated the holy cities of Mecca and Medina. As far as the writer was able to gather, however, from the natives themselves, the Asir is considered to be an entirely different district, although its inhabitants are nearly related to the Yemenis by blood. In fact, it may be said without much exaggeration that the present divisions of Arabia as marked upon the maps are but little in advance geographically of the ancient Greek and Roman arbitrary distinctions of Arabia Felix, Arabia Petræa, and Arabia Deserta. Even allowing for the widest limits claimed for the Yemen, the whole country lies between 42° and 46° east longitude and 12° and 20° north latitude.