It was intended to be the final bulwark of British Unionism but instead became famous for being the Scottish army garrison that never fired a shot in anger.

The 18th century Fort George protrudes into the Moray Forth, guarding Inverness from invasion from land and sea. It was built as the finest fortress in Britain specifically to evade capture in the aftermath of the Jacobite rising 1745 and as a base to house King George II’s army.

To mark the 250th anniversary of the star-shaped fortification, that took two decades to build, Historic Environment Scotland are holding the inaugural Festival at the Fort this weekend.

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The two-day celebration will feature a programme of family-friendly activity, historical re-enactment, music, dance and song.

Re-enactment performances will tell the story of the Jacobite risings and the building of Fort George. Visitors can also meet costumed characters in the history encampments and hear the stories of Jacobites as well as those who were involved in the construction of the fortress.

There will also be a 1940s Second World War zone, with tents and vehicles. Visitors will be able to find out about the important role Fort George as a training base.

Designed so that if it was attacked escape could be made by sea, Fort George was commissioned by King George II in the wake of the battle of Culloden, the final confrontation of the Jacobite uprising.

Even though it was built to thwart the supposed threat that saw it being built, the fort has not been attacked since it was built in 1748 and has remained a serving barracks since 1769.

Widely known as one of the most impressive artillery garrisons in Europe, the fortress was designed by Lieutenant-General William Skinner who also served as the first governor of Fort George, named after the King who ordered it to be built.

General Skinner mapped out the complex layout of ramparts, bastions, ditches and firing steps.

Defences were heavily concentrated on the landward side of the promontory – the direction from which a Jacobite assault was expected. Long stretches of rampart - some more than 1km long - and smaller bastions protected the remaining seaward sides.

Built by the Adam brothers, John, Robert and later James, known for their neo-classical style, acting as contractors, overseeing around 1,000 soldiers who provided labour and defended the site against attack. By 1757 the main defences were in place, and Fort George was finally completed in 1769.

Later in the 1700s, when the Jacobite threat was over, the fort became a recruiting base and training camp for the rapidly expanding British Army. Many a Highland lad passed through its gates on his way to fight for the British Empire across the globe.

Between 1881 and 1964, the fort served as the depot of the Seaforth Highlanders.

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Fort George is currently the home of the Black Watch, 3rd Battalion The Royal Regiment of Scotland (3 SCOTS).

The original budget for the fortress to be built and equipped was the kingly sum £92,673 19s 1d but more than doubled to £200,000, the equivalent of nearly £1bn.

The boundary walls of the fort housed accommodation for the governor, officers, an artillery detachment and a 1,600-strong infantry garrison. It also housed more than 80 guns, a magazine for 2,672 gunpowder barrels, ordnance and provision stores, a brewhouse and a chapel.

The fort's former Lieutenant Governors’ House is now home to the Highlanders Museum, Scotland’s largest regimental museum outside Edinburgh which houses an impressive collection of arms including bayoneted muskets, pikes, swords and ammunition pouches.

The Fort George that remains today is a rebuilding of an original site built in 1727 in Inverness. The first Fort George could house 400 troops near the River Ness on the site of the medieval castle which had been rebuilt as a citadel by Oliver Cromwell.

During the 1745 rising the fort was seized by the Jacobites, who had it blown up in 1746 to prevent the Hanoverians from using it as a base.

In 2016, Sir Michael Fallon, defence minister at the time, announced that Fort George would be closed down in 20132, along with 15 other seven other military sites in Scotland.

Gillian Urquhart, Events Manager at HES, said: "Fort George is one of the most outstanding fortifications in Europe. This is a fantastic chance for anyone who has never visited before to discover why and how it was constructed and find out more about its present-day use."

Festival at the Fort takes place at Fort George from 12pm - 4pm on Saturday 10 and Sunday 11 August. The site is open from 9.30am – 5.30pm.

Entry to the event is included in the normal admission price.