Defensive elements were central to the military strength of Fort Mackinac. When the British built the fort between 1779 and 1781, Lieutenant Governor Patrick Sinclair designed it with walls of earth, stone, and wooden pickets. Cannon platforms on the south wall protected the harbor and village. On the north side, British troops dug a defensive ditch and constructed two half-bastions, fortified cannon positions that allowed soldiers to trap attackers in a crossfire as they approached the walls. Sinclair also added a V-shaped outer wall, known as a ravelin, to complete the northern defenses. Remains of these original British defenses are still visible just outside the fort walls.