The three forts strung along the Great Glen -- Fort George near Inverness, Fort Augustus in the middle, and Fort William at the southwestern end -- were the British government's answer to Highland unrest. Built in the 1720s as part of General Wade's program of military roads and garrisons, they were designed to project crown authority into territory that had resisted central control for centuries. Fort Augustus occupied a strategic position where the Great Glen narrowed between Loch Ness and Loch Oich, controlling the route between the eastern and western Highlands. But the fort's defenses had been designed for a different era. By 1746, its walls and barracks were poorly suited to withstand a determined assault by a force with artillery, and the Jacobites, though losing the broader campaign, had both determination and guns.

The siege began on 22 February 1746. Colonel Stapleton, a professional soldier in the Irish Brigade -- Irish Catholics who served in the French army -- brought military expertise that complemented the raw fighting spirit of the Highland clansmen. The Cameron and MacDonald warriors who made up the bulk of his force had personal reasons to fight: their homelands lay in the surrounding glens, and the fort represented the occupying power that threatened their way of life. The garrison, outnumbered and aware of Cumberland's own assessment of the fort's weaknesses, held out for roughly a week before surrendering on 1 March. The capture was clean by the standards of the time, with the garrison allowed to depart. Fort George to the northeast had already fallen even more easily, its commander choosing surrender over a fight he could not win.

Stapleton and the Jacobite leadership moved on from Fort Augustus to besiege Fort William, the last government strongpoint in the Great Glen. But Fort William held, its defenses stronger and its garrison more resolute. The failure to take Fort William left the Jacobite supply lines insecure and their strategic position weakening by the day. Within weeks, the Jacobite army would face Cumberland's forces at Culloden on 16 April 1746, where the rising was destroyed in less than an hour. The capture of Fort Augustus, though a tactical success, proved to be one of the last Jacobite victories of the '45. After Culloden, Cumberland reoccupied Fort Augustus and used it as his headquarters while his troops systematically brutalized the surrounding Highland communities. The fort that the Jacobites had captured would become the base from which their culture was dismantled.