St Breock Downs Monolith (or St Breock Longstone; Cornish: Men Gurta[1]) is the largest and heaviest prehistoric standing stone in Cornwall, England.

The stone is made from the local Devonian shale which has extensive feldspar veining,[3] and it is estimated to weigh around 16.5 tonnes.

[3] The excavation showed that the stone stood in a setting of quartz pebbles below which were two small hollows.

[3] The stone is mentioned in antiquarian records as early as 1613, and was later adopted as a St Breock parish boundary marker.

[5] Media related to St Breock Downs Monolith at Wikimedia Commons