The Russian High Command understood the situation very well. Their aim was to keep von Hindenburg busy on the Niemen, while their armies in the south were overwhelming the fleeing Austrians. Von Hindenburg was deceived, and continued his advance until he got into serious trouble. His movement had begun on September 7th; his army consisted of the four corps with which he had won Tannenberg, and large reinforcements from Germany, including at least one guards battalion, and a number of Saxons and Bavarians. The country is one vast mixture of marsh and lake and bog. The roads are few, and advance must therefore be slow and difficult. Rennenkampf made no attempt to delay him beyond a little rear-guard fighting. The German army reached the Niemen on September 21st, and found behind it the Russian army in prepared positions, with large reinforcements from Vilna. The river at this point was wide and deep, and hard to cross. The battle of the Niemen Crossings was an artillery duel. The Russians quietly waited in their trenches to watch the Germans build their pontoon bridges. Then their guns blew the bridges to pieces. Thereupon von Hindenburg bombarded the Russian lines hoping to destroy the Russian guns. On Friday, the 26th, his guns boomed all day; the Russians made no reply. So on the morning of the 27th he built bridges again, and again the Russians blew them to pieces. On the 28th he gave the order for retreat. He realized that the game wasn't worth the candle; he might easily be kept fighting on the Niemen for months, while the main armies of the Russians were crossing Austria. Von Hindenburg conducted the retreat with a skill which came to him naturally from his knowledge of the marshes. Rennenkampf followed him closely, keeping up persistent attacks through the woods and marshes. The path of the retreating army lay through the forest of Augustovo, a country much like that around the Masurian Lakes, and there the Germans suffered heavy losses. Von Hindenburg managed, however, to get the bulk of his forces back across the frontier and continued his retreat to the intrenchments on the Masurian Lakes. The Germans lost 60,000 men in killed, wounded and prisoners, and von Hindenburg handed over the command of the German armies in East Prussia to General von Schubert, and hastened south to direct the movement to relieve the Austrians at Cracow. But quite as important as the campaign in East Prussia was the struggle in Galicia. When the war began the Germans contemplated merely defense in their own domain; such offense as was planned was left to the Austrians farther south.