Marshy ground made difficult the attack on their front, but, nevertheless, they seem to have been unable to prevent the Russians from piercing the screen before the crossing of the river had been completed. There was great slaughter. The Russians claimed that they took 30,000 prisoners. The artillery of the Russians was highly effective in shelling the bridges while the Austrians were passing over them in solid masses. Beside the large number of those killed by shell fire many were reported to have been forced into the water and to have drowned. Neither was there respite for the Austrians on the other side of the river, although, in theory, the forcing of the passage of the San by an invading army was considered an impossible task. Enormous sums had been spent by the Austrians in an attempt to make it impregnable. Along the upper or southern part of its extent it was protected by the powerful position of Przemysl and by Jaroslav. From there a light railroad, which had been built solely for strategic purposes, ran parallel and close to its left bank almost to the point where it joined with the Vistula. As they retired, the Austrians destroyed bridges behind them. But they were not able to destroy all, otherwise a few days' rest might have been vouchsafed the First Army. By quick work the Russians seized and maintained a hold on the bridge at Kreszov, on the frontier a few miles west of Tarnograd. As an official communique from Petrograd put it: "The Russians leaped across the river on the very shoulders of the retreating enemy." The victory on the San, September 12-19, 1914, may well be considered one of the most important of the campaign. There is no way of estimating the Austrian losses, over and above the 30,000 prisoners the Russians say they took, but they probably were heavy. Still more important was the fact that the Russians had broken down the barrier which the Austrians had sought to put between themselves and the invaders. Save for the fact that the Austrians were now in touch with their railroads, and for the moment within reach of security, being under the shelter of Cracow, their position within the triangle formed by the Vistula was no more safe than it had been when they were above it. The Russians reported that within that triangle they seized an enormous amount of supplies of every kind. Moreover, with the advance on Krzeszov, the last of the invading Austrians had been forced from Russian soil. No longer was an enemy left in the provinces of Podolia or Volhynia.