Meantime, the Army of the Narev, under General Samsonov, was advancing through the country west of the Masurian Lakes. On the 20th his vanguard came upon a German army corps, strongly entrenched at the northwest end of the lakes. The Germans were defeated, and fled in great disorder toward Koenigsberg, abandoning their guns and wagons. Many prisoners were taken, and the Russians found themselves masters of all of East Prussia except that inside the Koenigsberg line. They then marched on Koenigsberg, and East Prussia was for a moment at the mercy of the conqueror. [Illustration: COSSACKS OF THE DON ATTACKING PRUSSIAN CAVALRY In a fierce encounter near the Dneister River the Russian horsemen put to flight the Kaiser’s best soldiers.] Troops were left to invest Koenigsberg, and East Prussia was overrun with the enemy. The report as to the behavior of these troops met with great indignation in Germany; but better information insists that they behaved with decorum and discretion. The peasantry of East Prussia, remembering wild tales of the Cossacks of a hundred years before, fled in confusion with stories of burning and slaughter and outrage. Germany became aroused. To thoroughly understand the effect of the Russian invasion of east Prussia, one must know something of the relations of that district with the German Empire. Historically, this was the cradle of the Prussian aristocracy, whose dangerous policies had alarmed Europe for so many decades. The Prussian aristocracy originated in a mixture of certain west German and Christian knights, with a pagan population of the eastern Baltic plain. The district was separate from Poland and never fell under the Polish influence. It was held by the Teutonic knights who conquered it in a sort of savage independence. The Christian faith, which the Teutonic knights professed to inculcate, took little root, but such civilization as Germany itself had absorbed did filter in. The chief noble of Borussia, the governing Duke, acquired in time the title of King, and it was here, not in Berlin, nor in Brandenburg, that the Hohenzollern power originated. East Prussia, therefore, had a sentimental importance in the eyes of the Prussian nobility. The Prussian Royal House, in particular, had toward this country an especial regard. Moreover, it was regarded by the Germans as a whole as their rampart against the Slav, a proof of the German power to withstand the dreaded Russian. That this sacred soil should now be in the hands of a Cossack army was not to be borne. The Kaiser acted at once. [Illustration: THE EASTERN FIGHTING ZONE]