Closer and closer the girdle was drawn. Every day the German advance progressed. In the evening of August 19, 1915, Prince Leopold's forces crossed the Bug at Melnik and began to threaten the fortress from the northwest. Still closer to Brest-Litovsk Austrian troops belonging to Von Mackensen's group crossed to the north bank of the Bug near Janoff, while other parts of this group advanced from the south beyond Vlodava and forced the Russians to withdraw from the east bank of the Bug north of this town. On the Germans and Austrians pushed from all directions except, of course, the east. By August 20, 1915, the lower part of the Brest-Litovsk-Bialystok railway was crossed and the only railway leading out of the fortress toward the east, which at Shabinka separates into two branches, one to Minsk and another to Pinsk, seemed threatened. The German-Austrian advance from the south that day reached Pishicha, apparently directly toward the southern railroad from the fortress to Kovel and from there to Kovno and Kieff. From all sides now the circle around Brest-Litovsk was drawn closer. The important railroad center at Kovel was taken on August 24, 1915, and immediately the combined German and Austrian forces swung around toward the north along both sides of the road leading to Kobryn, east of the fortress and on the railroad to Pinsk. In the meantime heavy artillery had been brought up and began the bombardment of the fortress. During the night of August 25, 1915, the storming of the forts began. Austrian troops under General von Arz took the three forts on the western front, while a Brandenburg Reserve Corps attacked from the northwest and penetrated into the central forts. The Russians then evacuated the fortress. Its fall immediately imperiled the entire Russian positions and resulted in a general retreat of all Russian forces. The question for them now was no longer how long they were able to delay the enemy, but how much they could save out of the wreck. On the same day that saw the fall of Brest-Litovsk the Russians lost Bialystok, and on the next day, August 16, 1915, they evacuated the fortress of Olita on the Niemen, about halfway between Kovno and Grodno; the latter, the last of Russia's proud string of western fortresses of the first line, of course was now not only seriously threatened but had become practically untenable.