The Trident programme of the 18th century, and one of the last fortresses to be built before the gunners actually started to be able to hit anything. Hugely expensive deterrent, that was never used.
Three forts were built along the line of the Great Glen, in an attempt to prevent the Jacobites from pulling the dirk from the peat, the claymore from the thatch, and getting further than Derby the next time. Of course, Fort William and Fort Augustus are pretty pathetic by comparison.
Notable for having ranges where firing is at the mercy of every sheep-loving fatherless in a small boat who thinks that the buoys that mark the range danger area are nice to sail around, or tack through. Even more frustrating is the fact that you can see them, and are so tempted to give them bursts of the good news.
Before anyone gets teary-eyed and romantic about the Highlanders and the Jacobites, remember that most of the Scottish Regiments were on the winning side at Culloden. Think of it as an Old Firm match, and the LD for the troubles.