From their respective bases of York Factory and Fort William, the two major fur companies built a network of posts across western Canada. Such expansion was possible by utilizing the extensive river systems. Lake Winnipeg was the hub of the transportation system of both companies; from here the brigades could follow one of several routes according to their destination. The Red River system led to the southern posts, the two branches of the Saskatchewan to the more westerly posts, its northern branch reaching toward the mountain passes which gave access to the Columbia River. The northern posts situated along rivers which comprised the Arctic drainage basin were linked to the rivers of the Hudson Bay drainage basin by the strategic Methye Portage which was twelve miles long. As this map shows, posts were often built side by side at strategic points. The North West Company, however, was responsible for opening up most of the country. It pushed over the Rocky Mountains to establish posts along the Pacific Slope and also penetrated north into the Mackenzie Valley.
