Between August–December 1914, the overall picture on the eastern front displayed a dynamic equilibrium. In the north, German victories at Tannenberg and the Masurian Lakes had the Russians in retreat but, in the south, the Russians had achieved equally decisive victories over General Conrad’s Austro-Hungarian army in the Battle of Galicia and had surrounded and besieged the fortress of Przemysl. Not only did Conrad suffer devastating casualties, many of the Slavic foot soldiers surrendered, many offering to fight for the enemy. In the central front, exchanges were more balanced; seeking to capitalize on their successes in East Prussia the Germans had advanced to the Vistula, but were repulsed by a Russian counterattack. The Russian follow-up was in its turn checked by the Germans in December at the Battle of Lodz. These first campaigns convinced the Central Powers that the southern sector urgently needed German reinforcement.