In 1775, Henry took four large and twelve small canoes to explore the territory northwest of Lake Superior. Henry, Cadot, Peter Pond, the brothers Thomas and Joseph Frobisher then began to challenge the Hudson's Bay Company. Their group, with forty men, stopped at Cumberland House and afterwards built a trading post on Amisk Lake, the first post to be built north of the Saskatchewan River. In 1776, Henry set off by foot to Fort à la Corne, following the Saskatchewan River, and having satisfied his curiosity secured some furs from the Assiniboines. He then purchased 12,000 additional beaver skins from a trip up the Churchill River from the Chipewyans, and some of his last packs were forcibly acquired from Robert Longmoor, an agent for the Hudson's Bay Company. Laden with furs, Henry returned to Montreal and gave the governor, Sir Guy Carleton, a large map of the western region through which he had travelled.