The Great Glen Forts: Fort William, Fort Augustus and the Chain Across the Highlands

The strategic logic of the three-fort system

The Great Glen (Gleann Mòr; also Glen Albyn/Glen More) is a near-straight, fault-controlled valley slicing the Highlands from coast to coast — from Fort William on Loch Linnhe in the south-west to Inverness on the Moray Firth in the north-east, roughly 60–62 miles. It follows the Great Glen Fault and is largely filled by a chain of lochs — Loch Linnhe, Loch Lochy, Loch Oich and Loch Ness — with short rivers between them. For centuries this trench was the great natural corridor across the northern Highlands, and equally a natural dividing line between the north-west Highlands and the Grampians to the south-east.

That geography is precisely why the government fortified it. By planting three forts along the glen — Fort William at the south-west end, Fort Augustus at the centre (head of Loch Ness), and Fort George at the north-east (first at Inverness, later the great new fortress at Ardersier) — the state could sit astride the principal artery of Highland movement, split the Jacobite-leaning clans into more manageable blocks, and use the lochs and (from the 1720s) the linking roads to shuttle troops and artillery rapidly between garrisons. Smaller posts at Ruthven, Bernera (Glenelg), Corgarff, Braemar and elsewhere extended the web outward. Fort George's own detailed story — the vast artillery fortress at Ardersier begun after Culloden — is fully told on Card #31 and is only cross-referenced here.

This was, plainly, a military occupation. Northern Scotland after the risings was, in effect, subject to garrison rule; the forts were the lynchpins of that system, and their purpose was coercive control of an internal population deemed disloyal. Following the site's "accuracy over patriotism" standard, the Great Glen forts are best understood not as romantic Highland castles but as instruments of pacification.

Fort William: origins and history

Fort William has the longest and most tangled pedigree of the three. Its first incarnation was the Garrison of Inverlochy, an earth-and-turf pentagonal fort thrown up in 1654 by General George Monck, Cromwell's commander in Scotland, to hold about 250 of the New Model Army and to overawe Clan Cameron after the Wars of the Three Kingdoms. Its position at the confluence of the River Nevis and Loch Linnhe let ships resupply by sea, bypassing clan-controlled land routes — a decisive advantage that would matter again in 1746. The Gaelic name for the town, An Gearasdan ("The Garrison"), preserves this military origin.

Abandoned after the Restoration of 1660, the site was re-founded in 1690 by General Hugh Mackay of Scourie in the aftermath of the Jacobite rising of 1689. It was named Fort William after William III (William of Orange), while the adjacent civilian settlement was called Maryburgh after Queen Mary II. Per Historic Environment Scotland's records, the earthworks were begun in 1690 and the stone walls raised around 1698, with stone barracks, stores and a magazine completed by 1714 — a staged sequence that the popular "rebuilt in stone in 1690" shorthand blurs. It was from the governor's quarters here that Colonel John Hill was involved in the events leading to the Massacre of Glencoe in 1692, when Alastair MacIain of Glencoe came to Fort William on 31 December 1691 to swear the oath of allegiance and was turned away to Inveraray.

Fort William was not taken in the 1715 rising, and — importantly — the frequently repeated claim of a repulsed formal siege in 1715 is not well supported by authoritative records; the fort was garrisoned and pressured but the documented siege is that of 1746. In the '45, after Fort Augustus fell on 1 March 1746, Fort William became the last government-held position in the Great Glen. It was a strong, modern, triangular work using the head of Loch Linnhe as cover, heavily armed and — crucially — able to be reinforced and resupplied by sea. The defenders were supported by the sloop Baltimore and, from mid-February, the bomb vessel Serpent (both operating under Captain Thomas Noel), adding firepower the besiegers could not match. Under the resolute Captain Caroline Frederick Scott (who replaced the doubted Alexander Campbell on 15 March), the garrison of around 400 — two companies from Guise's, two from Johnson's and one of the Campbell of Argyll Militia — held out against an estimated 1,000 Jacobites. Jacobite artillery, poorly sited and lacking its heavy guns (stranded at Inverness for want of roads and horses), made little impression. The siege ran 20 March – 3 April 1746 and was abandoned as Cumberland's army moved; it is often called the last siege on the British mainland.

The fort's afterlife was one of slow erasure. Garrisoned until 1864, it was then decommissioned, partly dismantled and sold; the West Highland Railway acquired the site from 1889 and swept away most of the interior and landward defences for its yard and line (the West Highland Line reached Fort William in 1894). The surviving officers' block served railwaymen until 1935 and the last interior gable was demolished in 1948. Today sections of the north and west rampart survive up to around 6m high, including a round-arched sally port (sea-gate) and a demi-bastion; the fort's inner gateway was re-erected in 1896 at Craigs burial ground about 400m away. Interpretation boards by the Friends of the Old Fort explain the site, and the West Highland Museum in Cameron Square preserves panelling from the governor's room and other fort artefacts within its Jacobite collections.

Fort Augustus: origins and history

Fort Augustus sits at the strategic heart of the glen, at the head of Loch Ness on a peninsula between the River Oich and the River Tarff. The spot had been the Highland village of Cille Chuimein (anglicised Kilcumein/Kiliwhimin, "the church of Cummein"). After the 1715 rising the government erected a barracks at Kilcumein in 1716 (on the site of what became the Lovat Arms Hotel garden) to overawe the central Highlands. This proving inadequate, General George Wade began a far more substantial fort in 1729, to a design associated with the engineer Captain John Romer; it was not completed until 1742. It was named Fort Augustus after Prince William Augustus, Duke of Cumberland — the same prince who, as "Butcher" Cumberland, would later make the fort his headquarters for the post-Culloden reprisals. Wade even planned a town around it to be called Wadesburgh.

The new fort was a square work with a bastion at each corner, a surrounding ditch, covered way and glacis, and a small harbour for a patrol galley on Loch Ness; it could hold up to about 1,000 men in an emergency. But its design had fatal flaws for a siege: its walls were relatively weak and its defensive guns were mounted atop the bastions, exposed to fire, and it was overlooked by higher ground.

Those weaknesses told in 1746. After the Jacobites abandoned the siege of Stirling Castle in February 1746 they turned to the Highland forts. Fort George (Inverness) surrendered around 21 February; then Fort Augustus was besieged from 22 February. French regulars quickly seized the isolated old Kilcumein barracks, and Jacobite coehorn mortars scored a decisive hit — on the first day a shell blew up the fort's magazine, destroying one of its bastions. The garrison under Major Hugh Wentworth capitulated on 1 March 1746 without casualties (Wentworth was later court-martialled for surrendering too soon). The Jacobites then used artillery captured at Fort Augustus to move against Fort William. This is the key contrast for readers: Fort Augustus fell; Fort William did not. (Note: earlier, in December 1745, a government force of about 600 men from the newly raised Independent Highland Companies had retaken Fort Augustus from local Jacobite Frasers after a small skirmish — so the fort changed hands more than once during the rising.)

Repaired and strengthened after Culloden, Fort Augustus was garrisoned for another seventy years before being disarmed in 1818 as militarily redundant. The dilapidated fort was sold in 1867 to Thomas Fraser, 14th Lord Lovat; his son Simon, 15th Lord Lovat, granted the site to the English Benedictine Congregation in 1876, who built Fort Augustus Abbey and later a school over and around the fort. The abbey closed in 1998, and the site was subsequently converted into private apartments. The north-east bastion survives to full height and other fort fabric is incorporated into the former abbey buildings, though there is no general internal access; a wall of the earlier barracks survives in the grounds of the Lovat (Arms) Hotel.

General Wade and Major Caulfeild: the military-road programme

The forts were only as useful as the ability to move troops between and beyond them, and the Highlands had almost no proper roads. In 1724 George I sent Major-General George Wade to assess the problem; he reported that much of the Highland population was ready to rise, and recommended new forts, roads and bridges, and locally raised Independent Highland Companies to police the clans. Appointed Commander-in-Chief, North Britain, Wade began building in 1725.

Over 1725–1737 Wade oversaw, in the words of Historic Environment Scotland, "the construction of 250 miles of road and 40 bridges… built by labouring gangs, military engineers and estates staff." His signature routes included the Great Glen road from Fort William to Inverness (completed 1727), the Dunkeld–Inverness road (the line of today's A9), the Crieff–Dalnacardoch road, and the dramatic road over the Corrieyairack Pass (completed 1731) linking Fort Augustus to Speyside and Dalwhinnie — for a time the highest constructed road in Britain, climbing to 770m (2,526 ft) by a series of zig-zags. Among his bridges, the High Bridge over the River Spean (1736), with three great arches carrying the Fort William–Fort Augustus road high above a gorge, was among the most spectacular.

When Wade left Scotland in 1740, his former inspector of roads, Major William Caulfeild, took over and built far more than his famous predecessor — commonly reckoned at around 800–900 miles of road and hundreds of bridges — though the whole network is still popularly called "Wade's Roads." Standard scholarship (William Taylor's The Military Roads in Scotland) totals the whole programme at roughly 1,100 miles built between the 1720s and the 1760s (Wade around 250–300, Caulfeild the remainder), the largest civil-engineering effort in Scotland since Roman times.

Historians are clear on the dual character of this infrastructure. Its primary purpose was military and coercive — to project regular troops and siege artillery into any resistant glen quickly, stripping the Highlands of their topographical protection. The very predictability of the roads could cut both ways: it was on Wade's road to Fort William, at the High Bridge, that the first shots of the '45 were fired on 16 August 1745, when about a dozen Keppoch MacDonalds — Donald MacDonell of Tirnadris "with eleven men and a piper" — bluffed and routed two companies (85 men) of the Royal Scots under Captains John Scott and James Thomson marching from Fort Augustus to reinforce Fort William. Yet over the following century the roads also became the backbone of Highland civilian communication, trade and, eventually, tourism — an incidental civil legacy that grew out of a programme of control.

The '45 experience precisely clarified

Because the three forts are so often lumped together, their very different fates in 1746 are worth stating plainly:

• Fort George (Inverness): surrendered to the Jacobites around 21 February 1746 without a real fight (its governor, Major George Grant, was court-martialled). Covered in detail on Card #31.
• Fort Augustus: besieged 22 February – 1 March 1746 and captured after its magazine was blown up by mortar fire; surrendered by Major Wentworth.
• Fort William: besieged 20 March – 3 April 1746 and not taken; the garrison under Captain Caroline Scott held out and the Jacobites withdrew before Culloden.

This is the same standard of precision applied to Edinburgh and Stirling Castles on Cards #32–33: two of the Great Glen forts fell, one did not.

After the forts: Telford's canal and roads

established A different kind of occupation. Within sixty years of Culloden the state came back to the Great Glen with engineers rather than garrisons. In 1803 Parliament set up two commissions, one to build the Caledonian Canal through the glen and one to build Highland roads and bridges, with Thomas Telford as engineer to both. Julian Glover, in his biography Man of Iron (2017), describes the brief Telford was given in 1801 as one fit for a colonial administrator: fisheries, harbours, roads, new towns, a canal from sea to sea, and the defence of harbours against an enemy.

established Telford's verdict on Wade. Telford judged the military roads harshly. In his 1803 report he wrote that they ran "generally in such Directions and so inconveniently steep, as to be nearly unfit for the Purposes of Civil Life". His own roads were laid out with easier gradients for carts and cattle, and joined onto the surviving military network. Today most traffic along Loch Ness uses the northern lochside road built under the commissioners, not Wade's road on the south side.

established The canal as a war measure. The Caledonian Canal was sold partly on military grounds. During the war with Napoleon the government hoped it would let naval and merchant ships pass from coast to coast without rounding the Pentland Firth, out of reach of enemy privateers. Telford later referred to the "political circumstances" behind it. By the time it opened, on 24 October 1822, the war was long over, and at about 12 feet deep in places the canal was too shallow for warships.

established Fort William and Corpach. At the south-western end the canal leaves the sea at Corpach, just outside Fort William, through two sea locks, then climbs a staircase of eight locks after about a mile of cutting. This flight, at Banavie, is now known as Neptune's Staircase. The lock chambers were cut into rock with a Boulton and Watt steam engine pumping almost without a break. Telford's resident superintendents there were John Telford, probably a kinsman, from 1804 until his death in 1807, and then Alexander Easton, appointed at about twenty. John Telford found Fort William so remote that it held a market only twice a year, and in 1806 a storm there killed several workmen. On opening day the first steamboat through reached Fort William in the late afternoon, and fifty-seven guests dined until four in the morning.

established Fort Augustus. The old fort, disarmed in 1818, sat beside the canal's busiest works. One of Telford's first tasks for the road commissioners had been to gather a store of tools at Fort Augustus. When Telford, John Rickman and the poet Robert Southey toured the canal in 1819, the flight of locks up from Loch Ness was still being built, with a steam dredger, horse railways and lock-gate iron newly arrived from Derbyshire. The masonry contractor there, John Cargill, had worked on the canal since 1804.

shared Glengarry and the canal. Alexander Ranaldson Macdonell of Glengarry, whose clan land included Loch Oich at the canal's summit, fought the commissioners for compensation for two decades. Glover repeats the story that he once rode his horse into the loch after a boat carrying Telford. It is reported, not documented in detail.

Later history and current heritage status

Both forts have largely vanished as military structures but survive in fragments and in memory. At Fort William, the surviving ramparts, sally port and demi-bastion beside the railway and Loch Linnhe are a scheduled monument, brought to life by Friends of the Old Fort interpretation boards, with the relocated gateway at Craigs burial ground and fort panelling and artefacts in the West Highland Museum. At Fort Augustus, the fort is subsumed into the former Benedictine abbey (now private flats) at the hub of the village, alongside Thomas Telford's later Caledonian Canal and its flight of locks; the Caledonian Canal Heritage Centre and the Great Glen Way keep the site busy with visitors. Wade's and Caulfeild's roads and bridges — the High Bridge ruins near Spean Bridge, the Corrieyairack road, Garva Bridge, Whitebridge — survive as scheduled monuments and walking/cycling heritage routes, the most tangible relics of the whole system.

The forts and the English language

established The garrisons brought English into the heart of the Gaelic Highlands. The historical geographer Charles Withers, in Gaelic in Scotland 1698–1981 (1984), records that Fort William in 1735 had "many hundreds that understands not the Irish", and that by 1760 the town was largely English-speaking. In 1794 the traveller John Lettice recorded the common view of visitors that "nowhere in North Britain is English spoken with better pronunciation than in the line of the forts and particularly at Inverness".

shared The effect did not last unchanged. As Highlanders moved into the towns, Gaelic came back: in the 1881 census Fort William was 72 per cent Gaelic-speaking and Fort Augustus 70 per cent, among the most Gaelic towns on the mainland.

• The first shots of the 1745 rising were fired at a Wade bridge. The Highbridge Skirmish (16 August 1745) took place at Wade's High Bridge over the Spean, where about a dozen Keppoch MacDonalds bluffed 85 government soldiers into surrender — days before Prince Charles even raised his standard at Glenfinnan.
• Fort Augustus is named after "Butcher" Cumberland. The fort (and later the village) took its name from Prince William Augustus, Duke of Cumberland — who then used it as his headquarters for the brutal post-Culloden reprisals.
• The Jacobites captured Fort Augustus and turned its own guns on Fort William. Artillery taken when Fort Augustus's magazine exploded was hauled south for the siege of Fort William.
• Fort William held out partly because it could be supplied by sea. Royal Navy vessels on Loch Linnhe kept the garrison fed and reinforced while the Jacobites' heavy guns were stuck at Inverness for want of roads.
• The 1746 siege of Fort William is often called the last siege on the British mainland.
• Wade's Corrieyairack road was, for a time, the highest road in Britain, crossing the pass at 770m (2,526 ft) by a dramatic series of zig-zags.
• General Wade is name-checked in an early verse of "God Save the King," reflecting how his road-building was seen as a bulwark against the Jacobites.
• The fort at Fort William gave the modern town its name and its Gaelic name. An Gearasdan simply means "The Garrison."

• Fort William's construction dates. Popular sources variously date the Williamite fort to "1690" or "c.1698." Both are partly right: HES/Canmore support 1690 for the re-founding and naming and around 1698 for the stone walls. Treat "rebuilt in stone in 1690" as a simplification.
• A "1715 siege" of Fort William. The claim that Fort William withstood a formal siege in 1715 is weakly sourced and not corroborated by authoritative HES records. The fort was garrisoned and pressured, but the well-documented siege is that of 1746. Treat the 1715 "siege" as traditional/unverified.
• "Last siege on the British mainland." This standard label for the 1746 siege of Fort William is best read as the last siege of the Jacobite risings on the mainland; it is repeated by HES and widely accepted, but worth stating precisely.
• Fort Augustus's naming. It was named for Prince William Augustus, Duke of Cumberland (George II's son) — not, as occasionally muddled online, confused with the unrelated 18th-century Fort William Augustus on Grassy Island in Nova Scotia.
• Fort Augustus demolition vs reuse. Unlike Fort William, most of Fort Augustus was not demolished but absorbed into the abbey and then converted to flats; its survival is by reuse, not clearance.
• The canal as a naval route. Do not say the Caledonian Canal served the navy in the Napoleonic Wars. It opened in 1822, after the war, and was too shallow for warships when it did.
• Distinct focus vs other cards. This card is not about the Highland Charge tactic (Card #28), the WWII Commando centre at Achnacarry (Card #29), or the detailed history of Fort George at Ardersier (Card #31). It treats the three-fort system's logic and gives Fort William and Fort Augustus their dedicated coverage.