THE circumstance of contiguity by which the southeastern end of the Balkan peninsula almost abuts against the extreme northwestern shore of Asia Minor provides an Eurasian ford which has facilitated human intercourse between Europe and Asia. The Dardanelles, the Sea of Marmora and the Bosporus constitute in reality a single strait. From Tertiary times to our day a normal and interdependent sequence of events has occurred on its site. In the prehuman period it is possible to trace land-fracturing followed by gorge-carving, valley submergence and strait formation. The post-human development witnesses conversion of the locality into an important section of one of the most widely traveled highways of mankind. Two main routes intersect each other in the dividing waters. Their courses leading from northwest to southeast and from northeast to southwest are at right angles to each other. In considering the value of the region as part of a much trodden route, it is necessary to ascribe proper importance to its lines of communication with Europe and Asia.
A Balkan zone of depression extending west and south of the Balkan uplift affords natural access between the valley of the Danube proceeding from the heart of Europe and the Dardanelles-Bosporus passage. It is constituted by the wide valley of the Morava and the narrower Nichava course leading to the Sofia basin, whence penetration into the Thracian plains is obtained by the Maritza valley.
The corresponding function for the Asiatic shore is performed by the valley of the Sakaria and to a lesser degree by the Pursak river depression—both trending westward from the high plateau of western Asia.
The main roads from the Bosporus or the Dardanelles to the Sakaria river valley skirt the shores of the straits and the Marmora as they follow a coastal lowland fringing the Dardanian and Bithynian heights. At Panderma, however, the old highway strikes inland slightly south of east to Brusa in order to avoid the elevated plateau intervening between the Marmora and Lake Abullonia. Thence, still following a line of least elevation, it wends its way towards the small harbor of Ghemlik (the Cius of Græco-Roman times) until beyond Isnik (ancient Nicæa of ecclesiastical fame) it debouches into the waters of the Sakaria.
The geological evidence at the shores of the Dardanelles and the Bosporus reveals the probable continuity of land at both points in a