The evacuation of Warsaw was the first step in the withdrawal from the apex of the Polish triangle which it was hoped the resistance of the sides would enable the Russians to complete without disaster; and a large garrison with adequate guns and ammunition was left at Novo Georgievsk to impede the German advance and hamper communications with their front. The greatest menace was on the north-west along the Narew and beyond in Courland where Von Buelow was preparing to strike behind the base of the triangle. On 10 August Von Scholtz breached the line of fortresses by storming Lomza, but Kovno was a much more critical point. It was the angle of the base, and its fall would not only threaten the base running south to Brest-Litovsk and all the Russian armies west of that line, but would greatly facilitate Von Buelow's sweep round beyond it and Vilna. The bombardment began on the day that Warsaw fell. Kovno was expected to hold out at least to the end of the month, but it fell on the 17th, and the general in command was subsequently sentenced to fifteen years' hard labour for his inadequate defence and absence from his post of duty. On the following day Von Gallwitz cut the line between Kovno and Brest at Bielsk, and on the 19th Novo Georgievsk fell to the howitzers of Von Beseler, the expert of Antwerp. Ossowiec, which had stood so well against the earlier German invasions, followed on the 23rd, and Von Beseler was brought up to give the coup de grâce to Brest. Its loss was perhaps inevitable after the fall of Kovno, but it completed the destruction of the base of the triangle and involved the withdrawal of the whole Russian line beyond the Pripet marshes which would break its continuity; and there was cold comfort in the fact that Ewarts got away with most of his troops and stores and that a Russian mine, exploded two days after their departure, destroyed a thousand Germans and set a precedent for similar machinations on their part when they retreated in the West. Fortresses now toppled down like ninepins. On the 26th Augustowo was evacuated and Bialystok captured. On the 27th Olita was abandoned and on 2 September Grodno. The Germans thus gained the whole line from Kovno to Brest, and things were going no better in the south. The fall of Lemberg had given the German right a position far to the east of their left, and Mackensen advancing from Lublin and Cholm had driven the Russians across the Bug at Wlodawa before Brest-Litovsk was taken. The marshes of Pripet were at their driest in August, and Mackensen encountered few obstacles as he pressed on from Brest to Kobrin and thence to Pinsk along the rail to Moscow. In Galicia Ivanov was pushed back to the Strypa and then the Sereth, and on the upper reaches of those rivers Brody was captured and two of the Volhynian fortresses, Dubno and Lutsk. Rovno itself was threatened, and with it the southern stretch of that lateral railway from Riga to Lemberg on which the Germans had set their hearts.