When the Germans entered Warsaw the German High Command had to decide what the next move was to be. Should they entrench on the ground already won, and make the line of the Niemen, the Narev, and the Vistula a great bulwark of defence which would defy all Russian counter-attacks for many a day to come, or should they push their armies forward? There were good reasons why a halt should be called on the river line. The troops were weary with long months of fighting, and badly needed rest. On the other hand, the Russian armies were not crushed, but it seemed likely that another big push would destroy them altogether. With Warsaw gone, the southern railway cut, and the Narev line crumbling, it appeared almost impossible for the Russians to escape. The army in Courland was almost within striking distance of the Petrograd railway, and once this was captured in the neighbourhood of Dvinsk and Vilna, the whole Russian front would be split up into separate armies, each of which might be destroyed. Another great effort, and the Tsar would be on his knees suing for peace. The die was now cast; the Germans decided to push forward. The Russians were in perilous plight; for on the right the Germans bade fair to envelop their armies, and in the centre von Mackensen was thrusting them back towards the Marshes of the Pripet, in which they might be caught. The Grand Duke's business was to get his armies away eastward, and to refuse at all costs to fight pitched battles. In this he succeeded, and by doing so wrote his name high on the roll of great generals. You will remember that the bridges across the Vistula at Warsaw had been blown up. Prince Leopold now collected a number of the thousand-ton barges which ply on the river, and constructed a floating bridge, across which he carried a railway line. By 10th August he began to advance; but he found himself constantly held up by Russian attacks, and he made but slow progress. By 16th August von Gallwitz was across the Petrograd line, and von Mackensen was within twenty miles of Brest Litovski. The Russians had already fallen back, and were lying in front of the railway from Ossowietz through Bialystok to Brest. They were, however, still holding out in front of the old city and fortress of Kovno.