Following Magdeburg, Tilly engaged the army of Gustavus Adolphus at the Battle of Breitenfeld on 17 September 1631, near the city of Leipzig, which he had reached after laying waste to Saxony. In the battle he was outmaneuvered by King Gustavus Adolphus and suffered 27,000 casualties. The Swedes’ maneuvering and accurate, rapid artillery fire caused his troops to break and flee. He withdrew, and political rivalries prevented Wallenstein from coming to his aid, so he turned to defence.