The Callanish stones on the Isle of Lewis are among the most complete and dramatic megalithic monuments in Britain, a cruciform setting whose alignments seem to track a rare event of the moon.
The setting
Erected around 3000 to 2500 BCE, the principal monument consists of a central ring of tall thin stones of Lewisian gneiss around a monolith nearly five metres high, with rows of stones radiating out to form a rough cross, and a small chambered cairn set within the ring. Several smaller stone circles stand nearby, so that Callanish, like other great megalithic sites, is the centre of a group rather than an isolated monument.
The lunar standstill
The site's alignments have been argued to relate to the major lunar standstill, an event on an 18.6-year cycle when the full moon rises and sets at its most extreme southerly points and, from Callanish, skims low along the southern hills before setting. To an observer at the stones the moon can appear to graze the horizon and briefly reappear, a spectacle the monument may have been built to frame. Such astronomical claims for megalithic sites, systematised by Alexander Thom, are treated with caution, but the Callanish alignment is among the more persuasive.
Buried and recovered
Over the centuries peat grew around the stones, eventually burying them to a depth of well over a metre; they were cleared in 1857, revealing the cairn at the centre. Local Gaelic tradition held the stones to be giants turned to rock for refusing to convert to Christianity, and remembered a figure who came to the stones at midsummer. The site is cared for by the Scottish heritage authorities and remains in use by modern Pagan and community observance.