There was, however, much danger in pushing far "into the bowels of the land." As the German lines of communication grew longer and longer, supplies would take more and more time to reach the armies, and there would be more and more chances that the line might be impeded or cut. Thousands of men would have to be taken from the firing-line to hold the railways and roads along which the convoys travelled, and thus the attack would gradually lose force, and at last be unable to resist a vigorous onset by the enemy. * * * * * Now we must return to the San, where the Russian armies were lying ready to retreat when the word was given. From the map on page 293 you notice that the Russian lines bulged out in front of Przemysl. Ivanov was prepared to give up this fortress, but not until he had cleared it of everything that might be useful to the enemy. In order to gain time he fought a holding battle in the centre and struck hard on the flanks. On the morning of 15th May his right began a three days' battle, in which the Austrians were well beaten, and after losing 30,000 men had to fall back. The enemy was caught in the open and the Russians plied the bayonet with deadly effect. On the borders of Bukovina the Russian left also had a success, and the enemy was driven back as much as thirty miles. But in the centre, where Mackensen was advancing, a very different state of things prevailed. The salient round Przemysl was fiercely attacked in three places, and its sides were driven in until the neck was less than ten miles across. Attacks were also made at two places farther north. When the Russian line was pierced at these points, the Austro-Germans were able to swing southwards towards the main railway, and the days of Przemysl were numbered. On 31st May the fortress fell, and at 3.30 on the morning of 2nd June von Mackensen entered the city. The Russians had held it a little over two months. The capture of Przemysl was a great feather in von Mackensen's cap, but it was no great prize. He found it little more than an empty shell. Guns, rolling stock, and supplies had been moved eastwards, and only a little booty fell into his hands. Why, you ask, did not von Mackensen push on more quickly and keep the Russians on the run? You must remember that his great weapon consisted of an enormous number of heavy guns which could only be moved slowly. As soon as the great machine lumbered up, the Russians were bound to retreat, but while it was slowly advancing to a new position, they were able to hold back the enemy on the wings and send away eastward all the valuable contents of the city. The great danger was always in the centre, where von Mackensen was making his terrible thrust; on the wings the Russians were able to delay the enemy.