A week before the Prussian Guard made its final charge at Ypres, Belgians reported the moving of masses of German troops away to the East. We have seen that the need was urgent, for Cossacks were already across the Silesian frontier, and Hindenburg required all the help he could get for his counter-offensive. He was planning an attack from Thorn up the Vistula primarily to strike the right flank of the Russian advance through Poland on Silesia and Cracow, and secondly to menace Warsaw. The command was entrusted to Mackensen, while Ruszky withstood the Germans with his right near Plock on the Vistula, his centre behind the Bzura, and his left stretching out towards Lodz. The Germans attacked all along the line on 18 November, but Ruszky's left seemed to afford the easiest prey; it had no natural line of defence, and Hindenburg's devastation during his retreat in October made the arrival of reinforcements from Ivanov farther south unlikely. Nevertheless Mackensen's most impetuous drive was against Ruszky's centre across the causeway at Piontek; it promised a dramatic success, and nearly ended in resounding disaster. The Russian centre was broken and the left thrust back upon Lodz, where it was attacked on three sides and seemed doomed to destruction. But the wedge was not sufficiently wide; it merely created a pocket in the Russian line. The sides held fast and Ruszky began to close the mouth. For three days, 24-26 November, the Germans fought desperately to get out, and at length the remnant succeeded, owing mainly to the lateness of reinforcements sent by Rennenkampf at Ruszky's request. Troops, however, were rapidly being rushed up to Mackensen's help, and on 6 December the Russian left withdrew from Lodz, the industrial capital of Poland with half a million inhabitants. The advantage of the retirement was to straighten the Russian line in face of the determined effort which Hindenburg was bent on making to secure Warsaw as a Christmas present for the Kaiser (see Map, p. 146).