They knew--none better--that Cracow was the key-fortress of Eastern Europe. If it fell, the Russians would be able to advance both into Germany and into Austria. Forty miles west of Cracow they would be in Silesia, the largest and most important manufacturing area of Germany, and the seat of its chief coal and iron mines. One-quarter of all the coal mined in Germany comes from Silesia, and it has some of the richest zinc deposits in the world. Its chemical and textile manufactures are the most extensive in all the Fatherland, and it has well been called the German Lancashire. If the Russians could enter Silesia and begin to lay waste its crowded industrial towns, a blow would be struck at the very heart of Germany. Berlin, too, would be in peril, for a road to the capital would be opened along the river Oder and behind the line of frontier fortresses. The capture of Cracow by the Russians would not only imperil Germany, but it would make them complete masters of Galicia. You already know what a very important part petrol plays in modern warfare. Motor cars, aeroplanes, and submarines must have petrol, or they cannot move. The petroleum of the world is chiefly found in America, round about Baku on the shores of the Caspian Sea, in Galicia, and in Rumania. The British navy had stopped the exports of petroleum from America; the Caspian oil fields were in the hands of Russia, and German supplies could only be obtained from Galicia and Rumania. The Galician oil fields, which are amongst the richest in Europe, lie along the northern slopes of the Carpathians. Once the Russians were masters of Galicia these oil fields would be in their hands, and the only other possible source of supply for the Germans would be in Rumania. Before the war began the Germans had provided themselves with huge supplies of petrol, but even in September 1914 these stocks were rapidly shrinking. Once the Russians captured Cracow they could begin the great task of pushing across the Carpathians into Hungary. You know that there is no love lost between the Hungarians and the Austrians. Should Hungary be threatened, and the Austrians be unable to send armies to drive back the invader, it seemed more than likely that the Hungarians would break away from the Germans and Austrians, and try to make peace on their own account. Nor was Hungary alone threatened. One hundred miles to the west of Cracow is the "Gap of Moravia," through which the river March flows to the Danube. It is the old highway from Germany into Austria, and along it runs the great railway which connects Silesia with Vienna. Thus the capture of Cracow would open a road not only to Berlin but to the capital of Austria as well. [Illustration: First Russian Advance towards Cracow.]