The relation of a region to the world depends in general upon its economic value. The importance of this southeasterly strip of the Balkan peninsula is therefore affected by its central location with reference to the continents of Europe, Asia and Africa. Between Paris and Bagdad, or the Cape of Good Hope, the overland route is continuous save for a short mile of water at the Bosporus and an equally insignificant crossing at the Isthmus of Suez, in the case of African travel. Herein lies the economic relation of this portion of the Balkan peninsula to the rest of the world. But the European coastland of the intercontinental strait separating Europe from Asia does not constitute a complete region. The Asiatic coast of the waterways must be taken with the European and a single district formed out of the Dardanelles, the Sea of Marmora and the Bosporus with their coasts and shores. This region is the threshold of Asia and conversely the entrance to Europe from the east. 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. This convenient gap is provided by the wide valley of the Morava and the narrower Nishava course which lead 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 in a less degree by the Pursak river depression--both trending westward from the high plateau of western Asia. The main roads from the Bosporus and the Dardanelles to the Sakaria river valley skirt the shores of the straits of the Marmora, as they follow a coastal lowland which fringes 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 winds towards the small harbor of Ghemlik (the Cius of Graeco-Roman times) until beyond Isnik (ancient Nicaea of ecclesiastical fame) it debouches into the waters of the Sakaria. These natural features connect the heart of Europe with the high plateaus of western and central Asia as well as with the fertile Mesopotamian lowland and the Indian peninsulas. The silk sent to Europe from eastern Asia in medieval days followed this road. The route has declined since the construction of the Suez waterway. Railway lines planned to connect Channel ports with the Gulf of Persia will restore the commercial value of the region. The value of the Bosporus as an avenue of trade remains unimpaired in modern days. It is the only maritime outlet for the export of the cereals and farm products of southern Russia and the oil of the Caucasus.