The battle of the San, one of the greatest of the war, opened on May 15, 1915. Jaroslav was in German hands; the Fourth Austro-Hungarian Army (Archduke Joseph Ferdinand) reached the western side of the San on the 14th; by the 16th the Austro-German armies held almost the entire left bank of the river from Rudnik to Jaroslav, about forty miles. They crossed at several points on the same day and enlarged their hold on the right bank between Jaroslav and Lezachow near Sieniava, which they captured. A German division arrived at Lubaczovka, due north of Jaroslav, and half of the Germanic circle around Przemysl was now drawn. The German plan was an advance in force from the Sieniava-Jaroslav front against the Przemysl-Lemberg railway, the most vulnerable point of the Russian line of retreat from the fortress. Fifteen bridges were accordingly erected over the San in that sector between May 20-24, 1915, across which the German battering ram was to advance on Przemysl. South of the town mounted patrols came into touch with Russian cavalry; four Austro-Hungarian and one German army corps were standing prepared between Dobromil and Sambor; Sambor was occupied by them. The Russians held the left bank close to the river from Sieniava to Jaroslav, and northward of the former and to the west as far as Tarnobrzeg. From Jaroslav their front ran in almost a straight line for thirty miles southeastward to the outer and northern forts around Przemysl, described nearly a complete circle around the western and southern forts to Mosciska on the east, thence south to Sambor, and from Sambor to Stryj. From Stryj eastward to the Bukowina the line remained unaltered. In that region Lechitsky and Von Pflanzer-Baltin had been conducting a campaign all by themselves; they were now resting, waiting, watching.
While great Germanic preparations for the capture of Przemysl were proceeding north of the town, the battle opened on Saturday, May 15, 1915, in the south, against the Russian front between Novemiasto and Sambor. Here the Austro-German troops were thrown against Hussakow and Krukenice to hack their way through trenches and barbed-wire entanglements in order to reach the Przemysl-Lemberg railway and thereby complete the circle. "At the cost of enormous sacrifices the enemy succeeded in capturing the trenches of our two battalions."