The Emperor, after a hunting trip across the Hungarian border in "a typical day in the wettest and coldest October in memory", fell seriously ill at the Favorita Palace, Vienna, and he died on 20 October 1740 in the Hofburg. In his "Memoirs" Voltaire wrote that Charles' death was caused by consuming a meal of death cap mushrooms. Charles' life opus, the Pragmatic Sanction, was ultimately in vain. Maria Theresa was forced to resort to arms to defend her inheritance from the coalition of Prussia, Bavaria, France, Spain, Saxony and Poland—all party to the sanction—who assaulted the Austrian frontier weeks after her father's death. During the ensuing War of the Austrian Succession, Maria Theresa saved her crown and most of her territory but lost the mineral-rich Duchy of Silesia to Prussia and the Duchy of Parma to Spain.