The Altar Stone is a recumbent central

megalith A megalith is a large stone that has been used to construct a prehistoric structure or monument, either alone or together with other stones. There are over 35,000 in Europe alone, located widely from Sweden to the Mediterranean sea. The ...

Stonehenge Stonehenge is a prehistoric monument on Salisbury Plain in Wiltshire, England, west of Amesbury. It consists of an outer ring of vertical sarsen standing stones, each around high, wide, and weighing around 25 tons, topped by connectin ...

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

, dating to Stonehenge phase 3i, around 2600 BCE. It is identified as Stone 80 in scholarly articles. Its name probably comes from a comment by

Inigo Jones Inigo Jones (; 15 July 1573 – 21 June 1652) was the first significant architect in England and Wales in the early modern period, and the first to employ Vitruvian rules of proportion and symmetry in his buildings. As the most notable archit ...

who wrote: :‘... whether it might be an Altar or no I leave to the judgment of others’.

Composition, origin, and situation

The Altar Stone is made of a purplish-green micaceous

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates) ...

and is thought to have originated from outcrops of the Senni Beds formation of the

Old Red Sandstone The Old Red Sandstone is an assemblage of rocks in the North Atlantic region largely of Devonian age. It extends in the east across Great Britain, Ireland and Norway, and in the west along the northeastern seaboard of North America. It also exte ...

Wales Wales ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

, though this has not been fully established. Stone 55 (a

sarsen Sarsen stones are silicified sandstone blocks found in quantity in Southern England on Salisbury Plain and the Marlborough Downs in Wiltshire; in Kent; and in smaller quantities in Berkshire, Essex, Oxfordshire, Dorset, and Hampshire. Geology ...

megalith) lies on top of Stone 80 (Altar Stone) perpendicularly, and is thought to have fallen across it. The Altar Stone weighs approximately six tons and (if it ever was upright) would have stood nearly two metres tall. Some believe that it always was recumbent It is sometimes classed as a

bluestone Bluestone is a cultural or commercial name for a number of dimension or building stone varieties, including: * basalt in Victoria, Australia, and in New Zealand * dolerites in Tasmania, Australia; and in Britain (including Stonehenge) * felds ...

, because it does not have a local provenance. Stone 80 was most recently excavated in the 1950s, but no written records of the excavation survive, and there are no samples available for examination that are established as having come from the monolith.

References

Stonehenge {{Wiltshire-struct-stub