To the north of the Gulf of Burgas, which is the westernmost extremity of the Black Sea, rise the fine porphyry mountains which terminate in the superb Cape of Emineh. They are sometimes described as an eastern prolongation of the Balkan, but erroneously, for the ancient lacustrine basin of Karnabat, now traversed by a railway, separates them from the system of the Hæmus. The granitic plateaux and mountains of Tunja and Stranja, which command the wide plain of Thracia on the north, are likewise separate mountain ranges. The Southern Balkan is, in reality, without ramifications or spurs, except in the west, where the mountains of Ikhtiman and of Samakov, so rich in iron ore and thermal springs, and other transverse chains, connect it with the mountain mass of the Rhodope. The upper basin of the Maritza River, enclosed between the Balkan and the Rhodope, has the shape of an elongated triangle, whose apex, directed towards the plain of Sofia, indicates the point of junction between the two systems. The whole of this triangular depression, with its lateral ramifications, was formerly occupied by lakes, now converted into bottom-lands of marvellous fertility. The passes near the apex of this triangle are naturally points of the highest strategical and commercial importance. Through one of them, still marked by ancient fortifications, and known as Trajan’s Gate, passed the old Roman highway, and there, too, the railway now in course of construction will cross the summit between the two slopes of the peninsula. This is the true “gateway of Constantinople,” and from the most remote times nations have fought for its possession. The numerous tumuli scattered over the neighbouring plains bear witness to many a bloody struggle.