A dozen men were dying of their own gunpowder smoke inside the Rock of Gibraltar, and the hole they cut to save their lungs became the most photographed feature in the whole fortress. That is not a flourish. It is, near enough, what happened in the summer of 1782, deep in the limestone of the North Face, while a Cornish miner turned soldier named Henry Ince led his choking party further into the mountain than anyone had ever gone before. Most visitors walk the Great Siege Tunnels in twenty cool, echoing minutes. They photograph the black cannon, peer through the gun ports at the airport runway and the isthmus far below, and move on to the next stop on the Upper Rock. Very few pause to learn that this whole network began as one man's idea, scratched out of the living rock with crowbars and gunpowder, or that its most celebrated feature was a happy accident born of near disaster. To understand Ince you first have to understand the desperation around him. The Great Siege of Gibraltar ran from the summer of 1779 to February 1783, roughly three years and seven months, making it the longest siege in British history. A British garrison of a little over five thousand men, under Governor General George Augustus Eliott, held the Rock against far larger Spanish and French forces, enduring scurvy, hunger and relentless bombardment. The crisis came in September 1782, when the Rock was pounded from the land and from a fleet of specially built floating batteries mounting well over a hundred heavy guns. Eliott's gunners answered with heated shot, set the batteries ablaze, and broke the assault. The defence held, but every clever advantage mattered, and one stubborn problem had nagged at the defenders for months. On the sheer northern face of the Rock there was a natural projection the soldiers called the Notch. From up there, guns could command the entire North Front and the narrow neck of land linking Gibraltar to Spain. The trouble was simple and maddening: there was no way to haul cannon up to it across the open, fire swept cliff. Governor Eliott is said to have offered a reward to anyone who could solve it. The answer came from Sergeant Major Henry Ince of the Company of Soldier Artificers, a unit raised in 1772 that was a forerunner of today's Royal Engineers. Ince was no career staff officer. Born around 1736, he had worked with his hands before he enlisted, and he understood rock the way few soldiers did. His idea was bold to the point of madness: do not climb the cliff, tunnel through it. The work was begun under the direction of a Royal Engineer, Lieutenant Evelegh, but the hands on the tools, and the imagination behind the scheme, were Ince's. > One man looked at an impossible cliff and proposed going straight through the mountain instead of over it. Work began on 25 May 1782. Ince led a party of around a dozen miners who attacked the limestone with sledgehammers, crowbars and gunpowder charges, advancing slowly through the heart of the Rock. There were no machines, no compressed air, no electric light. Every foot of gallery was won by hand, in heat and dust, by men who knew that one badly placed charge could bring the roof down on them. Progress was measured but real. By the time the siege ended in February 1783 the first gallery, named the Windsor Gallery, ran roughly 370 feet through the Rock and carried four guns. That was the very first tunnel ever cut into Gibraltar, and the seed of a network that grew steadily afterwards: under Ince's continued supervision the galleries reached close to four thousand feet by the end of the century, and far later the whole subterranean system of the Rock would stretch to many miles. It all traces back to this one tunnel and one Cornishman's idea. Here is the detail the crowds almost never hear. As the miners pushed deeper, the smoke and fumes from the blasting had nowhere to escape and very nearly suffocated them. To clear the air, they hacked an opening out through the side of the Rock to the open face of the cliff, simply as a ventilation shaft. When they looked at the hole they had made, they realised something. That vent, punched through the limestone to let the smoke out, framed a clean line of fire onto the ground below. It made an ideal embrasure for a cannon. So they mounted a gun there at once, without even waiting to reach the Notch, and cut more embrasures along the way. What had started as a plain transit tunnel became a line of gun galleries firing through the cliff face itself. > The most photographed feature of the tunnels began life as nothing grander than a vent for the smoke. The original plan was to reach the Notch and mount a single gun on top of it. By the time the diggers got there, in the summer of 1783, the siege was over, and a better idea had taken hold. Instead of a lone gun on an exposed crag, they hollowed the Notch itself into a broad chamber they named St George's Hall, later fitted with seven gun positions to sweep a wide arc across the isthm