The Germans, however, continued to be aggressive. Numerous raids were made at various points along the frontiers. In some quarters it was feared that these raids were the prelude to an early invasion. They were, as a matter of fact, designed to harass the Russians and keep them engaged while the Germans completed the mobilisation of the forces which were to defend Eastern Prussia and, if possible, invade Poland during the absence of the first line troops in the western theatre of war. These new forces were chiefly composed of the Landwehr, and comprised about twenty divisions of 20,000 men each, with thirty-one cavalry regiments and six batteries of artillery. This army, under the command of General von Hindenburg, was mobilised along a line about thirty miles from the frontier. Its right flank was protected by the marshes around Arys, while its left rested on Insterburg. Naturally it took some days to collect this army and prepare it for attack, and it was not until nearly the middle of August that the Germans were in a position to contemplate any serious advance. In the meantime the Russians, who were collecting considerable forces under General Rennenkampf, were able to throw back the cavalry which was harassing them, and to make a tentative advance over the Prussian frontier. On August 5th they entered Eydtkuhnen without opposition, and proceeded to advance towards the main German army. It was not until they reached Stalluponen that they encountered serious opposition. A sharp action resulted in the Germans being turned out of the town, leaving 200 dead and some machine guns. This advance on the part of Russia was hailed in the west as a definite invasion with the object of sweeping across Prussia to Berlin. It was nothing of the sort. Russia was only advancing because the Germans had not yet collected their full forces. Indeed, Russia was by no means ready, and she carefully refrained from pressing too far forward, pending the completion of her own preparations. After the affair of Stalluponen there was obviously the temptation to push forward. But this would have brought the attacking force dangerously near the main German army and dangerously distant from Russian support. The advance, therefore, ceased until stronger forces could be brought forward. The German preparations, too, were progressing, and they were able to deliver vigorous attacks on the small invading force. Numerous attempts were made to recapture both Stalluponen and Eydtkuhnen, but all were beaten back. Then, after an interval of about a week, the main Russian army, under General Rennenkampf pushed forward, and the advance into Eastern Prussia may be said to have definitely begun.