The Recumbent Stone Circle (RSC) is Aberdeenshire's unique contribution to the tradition of erecting rings of standing stones which was current in certain parts of Britain and Ireland during the third and second millennia BC.
Up to 99 examples have been recorded, with diameters ranging from 18.2 m to 24.4 m.
The distinctive feature of the RSC is the massive slab, laid recumbent on its side in the south-western or southern arc of the ring, and flaked by the two tallest stones of the circle. The recumbents average 24 tons in weight and were carefully levered and chocked-up to ensure that their upper surface was as level as possible.
It is believed that the recumbent and flanking stones form a kind of false horizon or frame through which to view the rising or setting of the major standstill moon that occurs every 18.6 years. At that point, the moon dips towards the recumbent. On 12 of the RSCs, decoration in the form of cupmarks (cup-shaped hollows between 10 and 50 mm in diameter) have been found, clustering at points (the recumbent, flankers or immediately adjacent stones) where the major standstill moon rises or sets.
http://www.aberdeenshire.gov.uk/archaeology/special/recumbent.asp