Follow the dotted line which shows the boundary between the two countries. You see that it zigzags south, then curves west, and straggles southward again to the border of Austria. As a rule, the boundary line between two countries follows, partly or wholly, some such natural barrier as a range of mountains or the course of a river. The Russo-German boundary, however, runs along neither mountains nor rivers. There are no mountains until you reach the Carpathians, about three hundred and eighty miles south of Königsberg; the whole region is a flat plain with scarcely a hill to break its monotony. Innumerable rivers wind their way across the country, and in wet weather overflow their banks and turn wide districts into one vast slough. The boundary line, however, does not follow these rivers, but cuts right across them. The dotted line which marks off Russian from German territory is purely artificial, and for this reason we may almost leave it out of account. You will notice that the great river which flows right across this region is the Vistula, which we will now follow from its source to the German boundary near Thorn. So widespread are the various arms of this river, that we might call the region the "Land of the Vistula"--the name by which Poland was known of old. The river rises in Silesia, on the northern slopes of the Carpathians. It flows through a mountain valley, and then turns east and north-east, and forms part of the frontier between Austria and Germany. Next it runs through the Austrian territory of Galicia, and passes by the old Polish capital of Cracow. Let us pause a moment and see something of this historic city. You notice, at once, that it blocks the road along the Vistula valley into Silesia, and that an invader must capture it before he can proceed to enter that province. Cracow has been a strong fortress for two and a half centuries, and now is surrounded by a circle of forts which the Austrians have strongly garrisoned. For two and a half centuries it was the capital of Poland. The finest of its thirty-nine churches is the Cathedral of Stanislaus, which stands on a rocky hill to the south-west of the old town. It was the crowning-place of the Polish kings, and within its walls are the tombs of several of the great Poles of history. Paintings, sculptures, and other objects of art adorn the cathedral, which dates from the middle of the fourteenth century. There is also a university with a rich library, and a Polish museum of art. About two and a half miles to the north-west of the city is a mound of earth a hundred feet high, which was thrown up between 1820 and 1823 in honour of Kosciuszko,[26] the great Polish hero. Because of its position, Cracow is the natural market for the exchange of goods between Silesia, Hungary, and Russia. There are coal and zinc mines in the neighbourhood.