Just as the British-American War of 1812 began, David Thompson, a leading North American mapmaker, explorer, and travel writer, went to Montreal for the first and only time. Forty-two years old, he had completed explorations and surveys of the West from Hudson Bay to the mouth of the Columbia, from the Mississippi and the Missouri to Lake Athabasca. Five years later he began an additional eleven strenuous years as astronomer (surveyor) for the British side in the British-American survey of the Canada-U.S. boundary, working on the Ontario section, stretching between St. Regis (near Montreal) and the Lake of the Woods. After the American astronomer resigned, Thompson acted for both powers. John J. Bigsby, a physician attached as naturalist and secretary to the British commission, described Thompson and his story-telling ability: "He was plainly dressed, quiet, and observant.... His speech betrayed the Welshman.... No living person possesses a tithe...