Before the lighthouse, before the wrecks, Bishop Rock was already a Cornish name and a Cornish punishment. The Cornish called it Maen Escop in 1284 - 'Bishop's Stone' - and in the late 13th century, when the Isles of Scilly were under the manorial control of John de Allet and his wife Isabella, the rock served a judicial purpose. Anyone convicted of felony was to be taken there, left with two barley loaves and a pitcher of water, and abandoned until the sea swallowed him up. Four kilometres west of the last land, at the mercy of Atlantic swell on every side, this was not a place of trial but of disposal. Whether the sentence was ever literally executed is uncertain - the record is medieval and short - but the geography fits the cruelty. A man left on Bishop Rock would not have lasted past the next high tide.

An 1818 report had already proposed that a lighthouse like Eddystone be built here. Nothing happened for a quarter-century. Then Trinity House sent James Walker to survey in 1843, and in 1847 he began building. His first design was elegant and ambitious: a 120-foot tower of accommodation and light sitting on top of iron legs, so the Atlantic could pass through and leave the structure unbothered. The Atlantic disagreed. Before construction was even complete, a storm took the iron-leg tower out completely. Walker started over in 1851, this time with solid granite. Resident engineer Nicholas Douglass and his sons James and William spent seven years coursing stone onto stone. No one died on the build. The light went on for the first time in 1858. And then the storms began.

Walker's granite tower stood, but only barely on its own terms. In ordinary weather the keepers reported the lighthouse trembling hard enough that objects walked off shelves and the optic itself fractured. The wick burned, the fog bell rang every ten seconds, and inside the tower the men lived with the building flexing around them. Then came April 1874. A succession of 120-foot waves struck the tower in series, smashing the reinforced glass of the lantern and sending the Atlantic itself down the staircase into the living quarters. James Douglass, by now Engineer-in-Chief at Trinity House, returned with men and broad iron bands. They bolted these through the stonework like the hoops of a barrel, hoping to hold the lower courses together. The storms of 1881 answered that, too: granite blocks the size of crates were torn away from the masonry just above the waterline. Douglass came back, looked at his patched lighthouse, and decided patches were no longer enough.

What James Douglass designed and his son William Tregarthen Douglass carried out at Bishop Rock between 1883 and 1887 is one of the strangest pieces of engineering in British civil history. They did not pull Walker's tower down. They built a second tower of massive granite courses fully around it, dovetailing each new block into the original masonry, then removed Walker's old lantern and floors and added forty more feet on top. The result is a lighthouse inside a lighthouse, with a new pair of hyperradiant Fresnel lenses arranged in five paired panels each, flashing twice a minute. It first lit on 25 October 1887, and at 49 metres it ties Eddystone for tallest in England. Keepers lived inside it for a century, hauled in and out by ropes from boats rolling far below, rappelling from the lamp gallery before a helipad was added. In 1973 the BBC made a documentary about a sixty-day tour of duty. In 1975 the children's programme Blue Peter sent Lesley Judd up; her harness slipped during the rope transfer and only her grip kept her in the air. Today the light is automated, the keepers gone, and Douglass's reinforcement still holds. The Atlantic still tries.

Trinity House crews called Bishop Rock the King of the Lighthouses, and the title fit because of what the rock had to bear. Bishop Rock marks the eastern terminus of the great North Atlantic shipping route - the western end being the entrance to Lower New York Bay - and for most of the 20th century, this was the line ocean liners crossed when competing for the Blue Riband, the transatlantic speed record. The Mauretania and the Queen Mary and the United States all rounded this light. Five kilometres east of Bishop Rock lies the Gilstone Reef, where in 1707 HMS Association went down in the worst British naval peacetime disaster - nearly 2000 men dead because nobody knew where they were. The light Douglass built was a direct descendant of that catastrophe: a stone marker, planted at the western edge of the known world, that said in the simplest language an empire knew - here. We are here. You are here. Don't come closer.