The retreat relieved the Russians of a great embarrassment. Its capture was considered in Germany as a great German victory, and at this time von Hindenburg seems to have felt that he had control of the situation. His movement, to be sure, had not interfered with the Russian advance on Cracow, but Warsaw must have seemed to him almost in his power. He therefore concentrated his forces for a blow at Warsaw. His first new movement was directed at the Russian right wing, which was then north of the Bzura River and east of Lowicz. He also directed the German forces in East Prussia to advance and attempted to cut the main railway line between Warsaw and Petrograd. If this attempt had been successful it would have been a highly serious matter for the Russians. The Russians, however, defeated it, and drove the enemy back to the East Prussian border. The movement against the Russian right wing was more successful, and the Russians fell back slowly. This was not because they were defeated in battle, but because the difficult weather interfered with communications. There had been a thaw, and the whole country was waterlogged. The Grand Duke was willing that the Germans should fight in the mud. This slow retreat continued from the 7th of December to Christmas Eve, and involved the surrender of a number of Polish towns, but it left the Russians in a strong position. They were able to entrench themselves so that every attack of the enemy was broken. The Germans tried hard. Von Hindenburg would have liked to enter Warsaw on Christmas. The citizens heard day and night the sound of the cannon, but they were entirely safe. The German attack was a failure. On the whole, the Grand Duke Nicholas had shown better strategy than the best of the German generals. Outnumbered from the very start, his tactics had been admirable. Twice he had saved Warsaw, and he was still threatening Cracow. The Russian armies were fighting with courage and efficiency, and were continually growing in numbers as the days went by. During the first weeks of 1915 while there were a number of attacks and counter attacks both armies had come to the trench warfare, so familiar in France. The Germans in particular had constructed a most elaborate trench system, with underground rooms containing many of the ordinary comforts of life. Toward the end of the month the Russians began to move in East Prussia in the north and also far south in the Bukovina. The object of these movements was probably to prevent von Hindenburg from releasing forces on the west. Russia was still terribly weak in equipment and was not ready for a serious advance. An attack on sacred East Prussia would stir up the Germans, while Hungary would be likewise disturbed by the advance on Bukovina. Von Hindenburg, however, was still full of the idea of capturing Warsaw. He had failed twice but the old Field Marshal was stubborn and moreover he knew well what the capture of Warsaw would mean to Russia, and so he tried again.