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.
Glance at the position of Kovno. You see (page 311) that it stands on the Niemen, at the point where the course of the river swings to the south. Should Kovno fall, the other fortresses on the Niemen would be in great peril, and the enemy would have a direct route to Vilna, where they would be in the rear of the Russians. On the day that Warsaw fell, the Germans were near enough to Kovno to begin the bombardment. For twelve days they rained shells upon the forts, while the infantry fought for the outworks. By this time the city had been stripped, and its valuable contents had been sent eastwards. Nevertheless it had to be held while arrangements were made for the Russian line to retire. The gunners in Kovno stuck to their posts for twelve desperate days, and all the time the big siege howitzers of the enemy played havoc among them. Nevertheless, the Russians held on, and, what is more, continued to work their guns.
By Sunday, 15th August, the forts were in ruins, and two days later the heroic garrison yielded. The Germans claimed 20,000 prisoners and over 200 guns. The Russians, however, were fully prepared for this loss. The holding of Kovno was a forlorn hope, and the men and guns in it were sacrificed to gain time.
The fall of Kovno meant that the Russian right must now retire, and a day later it was clear that the centre must retire too. The Germans had cut the railway to the north of Brest, and were now attacking the western forts of the stronghold. Next day Novo Georgievsk, which had been besieged for about three weeks and was now a huddle of ruins, had to yield, and 20,000 of the garrison, along with 700 guns, most of which had been rendered useless, fell into the hands of the Germans. Shortly before the surrender, a daring Russian aviator was entrusted with the maps and secret papers of the fortress. He ascended, and though furiously assailed by the anti-aircraft guns of the enemy, managed to fly clear and carry the precious documents into safety.