Porth Hellick Down is an area of downland on the east side of the island of St Mary’s in the Isles of Scilly.
Seven Scillonian entrance graves stand on the down in a general state of decay. The largest is the Great Tomb which has a 12m diameter and a central burial chamber 3m long and 1m high. An unroofed passage 4.2m long leads into the chamber at an angle. An encircling peristalith was destroyed during misguided restoration work by the Ministry of Works.
George Edward Bonsor Saint Martin excavated the Great Tomb in 1899 but found only Bronze Age pottery and reported that the tomb had already been cleared out.