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.

It also includes an ancient linear boundary and a prehistoric field system, which stretches across the northern and north western section of the Down.

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.

The Great Tomb was restored by the Ministry of Works, which included protecting the burial chamber with new turf.

The remains of the burial monument include part of the stone kerb and four capstones covering a coffin-shaped chamber.

[7] One of the entrance graves on Porth Hellick Down has a burial chamber that is constructed along a massive rock outcrop.

The burial chamber consists of a circular mound of stacked rubble, 13m in diameter and 1m high.

[8] Porth Hellick Down is the site of a prehistoric linear boundary which traverses its eastern slope.

Beginning at the eastern edge of the Down, the linear boundary stretches southeast to northwest for 17m, and then continues for another 23m.