His movement was further provoked by the Russian raid which had already advanced once more across the border to close on Tilsit, Insterburg, and Angerburg and well to the west of Lyck. Hindenburg was ever fertile in surprises on this familiar ground, and on 7 February his left, commanded by Eichhorn, drove the Russians back along the railway to Kovno, and within a week had occupied Mariampol. His right was also well across the frontier, marching on Grodno and Ossowiec. Superior forces and railway communications accounted for his success, and one Russian corps met with a disaster. But conditions on the Russian side of the frontier equalized matters. The Germans occupied Suwalki and Augustowo, and even crossed the Niemen at Drusskeniki between Olita and Grodno, while farther north they seized Tauroggen. But they were unable to cut the Kovno-Warsaw railway which ran but ten miles east of the Niemen, and Ossowiec farther south successfully stood a siege. By the middle of March Hindenburg had withdrawn his left and centre to cover the Prussian frontier. He had suffered considerably, but his right got off even less lightly. It was here that his main strategic objective lay. The thrust against the Niemen had been simply designed to drive the Russians out of Prussia and protect the left of the German offensive to the south on the Narew and Warsaw. Since the German failure in December a Russian army had been pushing slowly down the right bank of the Vistula in front of Plock. This movement was checked in February, and the Germans hoped by an advance from Mlawa to get across the Narew south of Pultusk. The centre of the Russian defence was at Prasnysz where eight roads meet, but the defending force was weak, and on 24 February the Germans captured the town. But the extreme Russian left made a heroic stand on the ridge between Prasnysz and Ciechanow against Germans in front and on both sides of them. Their resistance produced a situation somewhat resembling that at Lodz, for a rapid concentration of Russian reinforcements swept round to the help of the flank at Ciechanow, while others attacked the German left at Krasnosielce. The Germans encircling Ciechanow found themselves encircled at Prasnysz, and as at Lodz they had to fight desperately for three days to escape. They were assisted by the rudimentary equipment of the Russian forces; rifles and ammunition were scarce, bayonets and hand-grenades were none too plentiful, and some of the privates are even said to have fought with pitchforks. By such hand-to-hand and bloody warfare the Germans were driven out of Prasnysz back towards Stegna and Chorzele and their flank attack on Warsaw foiled. Ruszky's strategy and Russian heroism had gained one of the most singular victories in the war.