Porth Hellick Down is a Neolithic and Bronze Age archeological site located on the island of St Mary's, in the Isles of Scilly in Great Britain. The ancient burial monument encompasses a large cairn cemetery that includes at least six entrance graves, other unchambered cairns, and a prehistoric field system. The site is notable for having the largest assembly of surviving entrance graves. Site description Porth Hellick Down is located on the island of St Mary's in the Isles of Scilly, overlooking Porth Hellick Bay. The Neolithic and Bronze Age monument encompasses a large cairn cemetery containing several burial cairns, including at least six entrance graves. It also includes an ancient linear boundary and a prehistoric field system, which stretches across the northern and north western section of the Down. It is the largest surviving group of entrance graves in the world. The Great Tomb The largest and best preserved entrance grave on the ancient site is a Bronze Age grave (2000-1500 BC) located on the northwestern slope of Porth Hellick Down. The burial monument is situated close to the boundary of a prehistoric field system. The site was excavated by the antiquarian, George Bonsor in 1899. He named the entrance grave, "The Great Tomb". Earlier unrecorded excavations at the site had left the burial chamber empty, except for a piece of pumice and a few remnants of late Bronze Age pottery fragments. Bonsor's excavation is the first excavation in Scilly to be recorded in detail. The entrance grave sits on a low, circular platform. It consists of a mound that is 12.25m in diameter and up to 1.6m in height. The mound is retained by a kerb of large slabs. The burial chamber measures 3.5m by 1.5m wide and is 1m high. The grave is roofed by four capstones, 2.5m long and 1.25m wide. The burial chamber is D-shaped with two sides that incline westwards to intersect the inner end of the passage. The entrance passage is uncovered. The Great Tomb was restored by the Ministry of Works, which included protecting the burial chamber with new turf. The restoration project damaged the tomb when they removed the grave's outer kerb. It is now in the care of English Heritage. Selected monuments The entrance grave that is positioned the furthest west on Porth Hellick Down is the grave known as the "coffin grave". The remains of the burial monument include