A new army was gathered at Danzig, composed of the troops which had retired south-west, of the troops in Königsberg who were carried to Danzig by sea, and of reinforcements picked up in various parts of Germany. Later on several army corps were withdrawn from the western theatre of war. Altogether, von Hindenburg had about 150,000 men with which to begin the reconquest of East Prussia. He pushed forward from the line of the Vistula by the three railways which you see marked on the map. Along these three lines he rushed men, guns, and ammunition with great speed. [Illustration: Russian Infantry Officers saluting the Tsar. _Photo, Record Press._] You know that after the battle of Gumbinnen, Rennenkampf had advanced towards Königsberg, which is a very strong fortress with an open channel to the sea. He was now waiting for his siege train to arrive before beginning to attack it. Meanwhile Samsonov seemed as if he were bent on seizing the crossings of the Vistula. In order to do this he marched his troops south towards the important railway junction of Osterode, which stands on the margin of the lake region. He had five army corps--that is, about 200,000 men--but they could not deploy owing to the lakes and swamps which lay between the roads. His columns could not, therefore, come to the assistance of each other in case of attack. Von Hindenburg chose his ground with all the local knowledge and skill which was expected of him. He extended his line from Soldau to the north-west of Allenstein, so that his front was barred by lakes and swamps, over which his artillery had a great sweep of fire. He made his front still stronger by a string of forts built of trees cut down in the forests. Then he stood on the defensive, and Samsonov began to attack him. Towards the end of August there was a great struggle, which is known by the Russians as the battle of Osterode, and by the Germans as the battle of Tannenberg, from the name of a little village on a fir-clad dune in the neighbourhood. Von Hindenburg was in no hurry. He let the Russians wear themselves down by repeated attacks on his almost impregnable position, and then, when the right hour arrived, he counter-attacked. First, he forced back the Russian left, and cut it off from the one good road that led southwards to Russian Poland. Samsonov made a desperate effort to regain this road, and in order to do so was obliged to withdraw troops from his centre. He failed, and meanwhile his centre was pushed back into the terrible lake country to the east.