Rhine for the winter. The emperor mobilized his active forces in response to the French attacks, and began the process of calling up troops from the states of the empire, establishing a defensive line at Ettlingen, near Karlsruhe. In the spring of 1734 French maneuvers successfully flanked this line, and Prince Eugene of Savoy was forced to withdraw these forces to the imperial encampment at Heilbronn. This cleared the way for the French army under the Duke of Berwick to besiege the imperial fort at Philippsburg, which fell after a siege of two months in July 1734. Eugene, who was accompanied by Crown Prince Frederick of Prussia, made some attempts to relieve the siege, but never made any decisive attacks against the besieging army owing to its size and the relatively poor quality of the troops under his command. Berwick was killed by a shell at Philippsburg. French armies continued to advance along the Rhine, reaching as far as Mainz, but the growing imperial army, which came to include troops from Russia that had assisted with the capture of Danzig, was able to prevent France from establishing a siege there, and Eugene went on the offensive. A force of 30,000 under Friedrich Heinrich von Seckendorff crossed the Rhine and began pushing the French back toward Trier, defeating them at Clausen in October 1735, in one of the last battles before preliminary peace terms were reached. Italy French and Savoyard troops numbering over 50,000, under the command of Charles Emmanuel, entered Milanese territory as early as October 24, against minimal resistance, as the Austrian forces in the duchy numbered only about 12,000. By November 3, the city of Milan itself had surrendered, although the Austrian governor, Count Wirich Philipp von Daun, still held the fortress. France's great general, the Duke de Villars, joined Charles Emmanuel in Milan on November 11. While Villars wanted to move immediately against Mantua to secure the Alpine passes against Austrian reinforcements, Charles Emmanuel, mistrustful of his French allies and their dealings with Spain, sought to secure Milan. The army spent the next three months eliminating Austrian opposition from the remaining fortified towns in the duchy. Villars attempted to interest Don Carlos of Parma in joining the expedition against Mantua, but Carlos was focused on the campaign into Naples. Villars began to move against Mantua, but Charles Emmanuel resisted, and the army made little progress. In early