The researchers used a 3D computer model to analyze how the stone would have been illuminated throughout the different seasons four millennia ago, given that the tilt of Earth's axis has changed over time.

Their model showed that the slanted side of the stone would remain in permanent shadow during the winter, while it would have been illuminated only in the morning and afternoon during most of the summer. At midsummer, the sun would have lit the stone brightly all day.

"The use of shadow casting in monuments of this period is quite rare in the British Isles," Brown said. "But there are some examples including New Grange, Ireland, and some Clava cairns in the north-east of Scotland that have been proposed to include the intentional use of shadows. Both are associated to burial sites using the symbolism of a cyclic light and shadow display to represent eternity. Given the proximity of the Neolithic enclosure and possible ritual importance of this site, the Gardom's Edge monolith could be another such example."