Open skirmishing began on the outer defense works of Ticonderoga on July 2. By July 4, most of the American garrison was either at Fort Ticonderoga or nearby Mount Independence, the extensive fortifications on the Vermont side of the lake. Unknown to the Americans, their withdrawal from an outer defensive position cleared a way for the British to place artillery on the hilltop known then as Sugar Loaf (now Mount Defiance), whose heights commanded the fort. St. Clair withdrew the night after spotting British cannon on Sugar Loaf on July 5, and Burgoyne's men occupied the main fortification and the positions on Mount Independence on July 6. The uncontested surrender of the supposedly impregnable fort caused a public and political uproar. Although a later investigation cleared both Schuyler and St. Clair of any wrongdoing in the withdrawal, it caused the Continental Congress to replace Schuyler with General Horatio Gates as commander of the Northern Department of the Continental Army in August.