He now hurled his left against the Russian right wing, which lay north of the Bzura and well east of Lowicz. At the same time he increased his forces in East Prussia, and ordered them to march southwards from Mlava so as to cut the main railway from Warsaw to Petrograd. Had this move succeeded, the Russians would have been obliged to abandon Warsaw. Happily, a force advanced from the fortress of Novo Georgievsk, and drove back the Germans from East Prussia almost to their frontier. For the time being, the Russian right flank was secure. [Illustration: The Battle of the Bzura. Russian Field Artillery in Action. _By permission of The Illustrated London News._] The Russian wing just south of the Vistula was not, however, well placed to meet the other attack. It was cut into two by the river Bzura, and its communications were very bad. So, with great wisdom, Ruzsky determined to withdraw this wing behind the Bzura and its tributary the Rawka, which flows north to join the Bzura, a few miles east of Lowicz. Behind these rivers he would have good communications, by means of which he could easily bring up food, munitions, and reinforcements. So far the winter frosts had not been severe; there was only a thin coating of ice on the Polish bogs, and the Vistula and the Pilitza were still open for river traffic. Just when Ruzsky was planning his retirement a complete thaw set in, and in a few days the whole countryside was one slough of despond. The Germans advancing against his new position would have to flounder through many feet of mud to get at him. For a fortnight the Russians slowly fell back all along the line, and the towns to the west of the line of the Bzura and the Rawka were occupied by the Germans. By the 18th of December the Russians were in their new position, which soon proved itself to be as strong as the Allied position from Arras to Nieuport. The same kind of warfare now took place both in East and West. The Russians dug themselves in close to the shallow, muddy streams, and on the other side the Germans occupied the fairly high bank which marks the rim of an old channel. Attacks and counter-attacks were nightly incidents of the struggle. When the early darkness set in, the Germans, in close formation, crashed through the cat-ice along the shore, waded breast-high through the bitterly cold waters, and, in spite of severe losses, frequently gained the Russian bank. Sometimes they captured an advanced trench, but rarely could they hold it, and all the time they were losing heavily. Warsaw was only thirty-five miles away, and the roar of the German guns was clearly heard in the city. But there was no panic; the Russian lines were proof against every assault. By Christmas Eve the enemy was doing no more than hold his trenches. In East and West alike stalemate had set in. * * * * *