The importance of the situation can readily be appreciated when we reflect upon the geographical conditions. The entire section of the Tauric barrier between the Great Zab on the east and this valley of the Bitlis Su upon the west is composed of quite a network of lofty mountains, extremely difficult to cross. To these natural obstacles, which have played an important part in the history of these countries, are added dangers to traffic arising out of the lawlessness of regions which it has never been easy to police. Bitlis commands the approach to the first important natural passage between the districts about Lake Van and the Mesopotamian plains. The avenue of communication is taken down the valley of the Bitlis Su, and, crossing thence into that of the Keser Su, to the town of Sert, a distance of about forty miles. Although this route has not as yet been rendered passable to wheeled traffic, it is well adapted to caravans. At Sert you are already upon the fringe of the lowlands and in a different climate. On your one hand lies Diarbekr, with its ready access to the Mediterranean, and on the other Mosul, upon the navigable waterway of the Tigris, whence in any other country but Asiatic Turkey a service of first-rate steamers would afford quick access to the Persian Gulf. West of Bitlis there are several passages, the routes converging upon Diarbekr; but they are for the most part less accessible to the great plains of the tableland. It is therefore towards this avenue that the traffic is directed between widely distant centres of the plateau country and Aleppo or Baghdad.