The massive French fortress of Louisbourg on Cape Breton Island controlled access to Canada and provided a base for raiding the northern British colonies. It was thus a great triumph for New England when in June 1745 it was besieged and captured by an expedition organized by Massachusetts Governor William Shirley. Portraitist Peter Pelham (1697-1751) engraved this exquisite plan drawn by fellow Bostonian Richard Gridley, who had commanded artillery at the siege. The print is an example of how Pelham, Thomas Johnston, James Turner and other Boston engravers supplemented their income by applying their talents to mapmaking.