On August 5, 1914, Austria-Hungary, too, declared war against Russia, and the next day brought immediately engagements along the frontier of the two countries, which, however, did not develop seriously for some time. The Russian advance into East Prussia had reached Marggrabova by the 15th, and from then on proceeded fairly rapidly during the following week. Memel, Tilsit, Insterburg, Koenigsberg, and Allenstein--to name only a few of the more important cities of East Prussia--were either threatened with occupation by the Russian forces or had actually been occupied by them. The entire Mazurian Lake district in the southeast of the Prusso-Russian border region was overrun with Russian troops. But about August 22, 1914, Germany awoke to the danger of the Russian invasion. General von Hindenburg was put in command in the east, and in the battle of Tannenberg, which lasted from August 22 to 27, 1914, inflicted a disastrous defeat on the Russian armies, capturing tens of thousands of its soldiers and driving as many more to their deaths in the swamp lands of the Mazurian Lakes. Not only did this end for the time the Russian invasion of Germany, but the latter country's armies followed the retreating enemy a considerable distance into his own territory. But although such important points as Lodz and Radomsk were occupied during the last days of August and the first days of September, the German advance into South Poland quickly collapsed. In the meantime the Russians had successfully invaded Galicia, and by September 3, 1914, the Austro-Hungarians evacuated Lemberg. In the north, too, the Russian forces had resumed the offensive and once more were invading East Prussia. But they were again beaten back by Von Hindenburg on September 10-11, 1914, and, four days later, on September 15, 1914, suffered another serious defeat in the Mazurian Lakes. The Galician invasion, however, was meeting with great success. By September 16, 1914, the important Austrian fortress of Przemysl--sixty miles west of Lemberg--had been reached and its siege begun. By September 26, 1914, the Russians had reached the Carpathian Mountains and were flooding the fertile plains of the Bukowina, threatening an imminent invasion of Hungary itself.