The Danube flows through Bavaria, Austria, and Hungary, forms the boundary between Rumania and Bulgaria, and touches a small corner of Russian territory. It has sixty great tributaries, of which more than half are navigable. Step by step the volume of the main stream is augmented. We can see that for ourselves on our way through Europe. At Budapest, which is cut in two by the river, and where five handsome bridges connect the banks, we seem almost to be on a lake. The Elizabeth Bridge has a span of 950 feet. Farther down, on the frontier of Wallachia, the river is nearly two-thirds of a mile wide; but here the current is slow; creeks of stagnant water are formed, and marshes extend far along the banks. And at the point where the Rumanian railway crosses the Danube, we find at Chernovodsk a bridge over the river which is nearly 2-1/2 miles long and is the longest in all the world. Not far from here the waters of the Danube part into three arms and form a broad delta at the mouth. There grow dense reeds, twice as high as a man, on which large herds of buffaloes graze, where wolves still seek their prey, and where water-fowl breed in millions. If we look carefully at the map, we shall see that Central Europe is occupied mostly by the Danube valley, and that this valley, with its extensive lowlands, is bounded by the best-known mountains of Europe; in the north by the mountains of South Germany and Bohemia and the Carpathians, in the south by the Alps and the mountains of the Balkan Peninsula. [Illustration: MAP SHOWING JOURNEY FROM BERLIN TO CONSTANTINOPLE.] From Budapest the train takes us over the Hungarian plain, a very singular country, like a trough, for it is surrounded by mountains on all sides. There is abundance of rain, especially up on the mountain slopes. The winter is cold and the summer warm, as is always the case in countries far removed from the sea. Dust and sand storms are common, and in some parts blown sand collects into dunes. Formerly the Hungarian lowland was a fertile steppe, where Magyar nomads roamed about on horseback and tended their cattle and their enormous flocks of sheep. But now agriculture is extended more and more. Wheat, rye, barley, maize, rice, potatoes, and wine are produced in such quantities that they are not only sufficient for the country's needs, but also maintain a considerable export trade. Round the villages and homesteads grow oaks, elms, lime-trees, and beeches; poplars and willows are widely distributed, for their light seeds are carried long distances by the wind. But in the large steppe districts where marshes are so common the people have no other fuel but reeds and dried dung.