When the Innisidgen graves were built, the Isles of Scilly were not yet islands. Sea level was lower, and what is now an archipelago of more than a hundred specks of granite was a single low landscape of fields, heath, and ridges, surrounded by an enormous tidal lagoon. The Bronze Age communities who lived here grew barley on the lower ground and pastured cattle and the oxen that may have given the hill its name. They cremated their dead and tucked them into stone chambers called entrance graves, built so the doorway faced the rising sun or the open sea. The Scilly archipelago contains more of these graves than anywhere else in Britain - several dozen survive across the islands - and Innisidgen is among the finest preserved.

Two graves sit on Innisidgen Hill, distinct in style and condition. Upper Innisidgen, perched near the summit, is the larger and more intact of the pair, its circular mound nearly nine metres across and roofed by five great slabs that still hold the chamber dry inside. The doorway points roughly south-east. Lower Innisidgen, tucked down the northern slope, has lost most of its capstones and shows its age more honestly - two slabs remain of what was once a continuous roof, and the kerbstones that ringed the mound have shifted out of line. In 1950, someone slipped in and emptied the chamber of its earth and rubble fill without permission, robbing archaeologists of whatever the layers might have told them. What remains is the architecture itself: a small, deliberate, durable room for the dead.

The story did not end in the Bronze Age. The same scheduled monument boundary that protects the graves also covers a much later layer of human use - the remains of an English Civil War lookout or earthwork on the hill. When Parliamentary forces and Royalist holdouts fought over the Scilly Isles in the late 1640s, the high ground of Innisidgen offered exactly the kind of view that mattered: north across Crow Sound toward the Eastern Isles, and west toward Tresco and the deep water anchorages that ships had to use. Four thousand years after the first builders had finished their work, soldiers stood here scanning the horizon for sails.

Walk up from Hugh Town and you reach Innisidgen along a footpath that hugs the eastern coast of St Mary's, past granite tors, gorse, and outcrops scoured by Atlantic weather. Crow Sound spreads below to the northeast, a shallow channel that drains spectacularly at low tide. Beyond it lie the Eastern Isles, a scatter of uninhabited rocks and small islands where seals haul out. The two graves are quiet now, fenced lightly and managed by English Heritage, free to enter and explore. The capstones above Upper Innisidgen are some of the oldest worked stones a visitor to Britain can stand beneath. From this hillside, the line of human presence runs unbroken from the Bronze Age to the modern ferry pulling into Hugh Town below.