Arnold then traveled to Montreal where he served as military commander of the city until forced to retreat by an advancing British army that had arrived at Quebec in May. He presided over the rear of the Continental Army during its retreat from Saint-Jean, where he was reported by James Wilkinson to be the last person to leave before the British arrived. He then directed the construction of a fleet to defend Lake Champlain, which was overmatched and defeated in the October 1776 Battle of Valcour Island. However, his actions at Saint-Jean and Valcour Island played a notable role in delaying the British advance against Ticonderoga until 1777.