The first German objective was the city of Lodz. Von Hindenburg knew that he must move quickly before the Russians should get up reserves. His campaign of destruction had made it impossible for aid to be sent to the Russian armies from Ivanov, far in the south, but every moment counted. His right pushed forward and won the western crossings of the marshes. His extreme left moved towards Plock, but the main effort was against Piontek, where there is a famous causeway engineered for heavy transport through the marshes. At first the Russians repelled the attack on the causeway, but on November 19th the Russians broke and were compelled to fall back. Over the causeway, then, the German troops were rushed in great numbers, splitting the Russian army into two parts; one on the south surrounding Lodz, and the other running east of Brezin on to the Vistula. The Russian army around Lodz was assailed on the front flank and rear. It looked like an overwhelming defeat for the Russian army. At the very last moment possible, Russian reinforcements appeared--a body of Siberians from the direction of Warsaw. They were thrown at once into the battle and succeeded in re-establishing the Russian line. This left about ninety thousand Germans almost entirely surrounded, as if they were in a huge sack. Ruzsky tried his best to close the mouth of the sack, but he was unsuccessful. The fighting was terrific, but by the 26th the Germans in the sack had escaped. The Germans were continually receiving reinforcements and still largely outnumbered the Russians. Von Hindenburg therefore determined on a new assault. The German left wing was now far in front of the Russian city of Lodz, one of the most important of the Polish cities. The population was about half a million. Such a place was a constant danger, for it was the foundation of a Russian salient. When the German movement began the Russian general, perceiving how difficult it would have been to hold the city, deliberately withdrew, and on December 6th the Germans entered Lodz without opposition.