In October 1814, the American force of about 700 mounted riflemen under Brigadier General Duncan McArthur advanced rapidly as they left Detroit and raided the Thames Valley. The plan was to devastate the Grand River settlements and the region around the head of Lake Ontario which supplied flour to the British forces on the Niagara frontier. When the raid was launched, the British Army had just raised the Siege of Fort Erie on the Niagara River at the eastern end of the Niagara peninsula, and an American army under Major General George Izard was beginning a cautious advance from Fort Erie.