Stone circles are widespread throughout the British Isles and are believed to date from 2500 BC to 1000 BC. They are however hard to date precisely, vary considerably, and their exact purpose remains a mystery. Most are circular but some are elliptical showing an awareness of basic geometry. Most circles are single but some are grouped - others have central stones, outlying menhirs or holed stones that would also appear to be part of the stone circle system. There is some evidence to suggest that they were sites of observation of the apparent movements of the sun or moon. As the sun sets in a slightly different position with each passing day of the year, our ancestors would soon have realised that an accurate calendar can be constructed by carefully recording the daily change of alignment with some marker on the horizon. As the centuries passed it is likely that the circles became adopted or adapted for other purposes. It is not surprising that many have legends associated with them - typically of dancing maidens or musicians turned to stone for sabbath-breaking; probably indicating early Christian disapproval of the circles as ritual sites.