'The Sundial Stone', Knowth Megalithic Passage Tomb, Brú na Bóinne, Ireland
Knowth is a Stone Age Passage Tomb in the Boyne Valley in Ireland's Ancient East and together with Newgrange and Dowth are the principal sites of Brú na Bóinne UNESCO World Heritage Site. Knowth is the largest passage tomb of the Brú na Bóinne complex. The main mound is about 12 metres (40 ft) high and 67 metres (220 ft) in diameter covering about 1 hectare (2.5 acres). It contains two passages placed along an east-west line and was originally encircled by 127 kerbstones of which 124 are still in place.
The Great Mound was built over 5,000 years ago, probably after the construction of Newgrange and before the construction of Dowth. The Great Mound at Knowth is similar in size to Newgrange and is surrounded by 18 smaller satellite mounds. The Great Mound has two passages with entrances on opposite sides, the western passage is 34 metres long and the eastern passage is 40 metre long, ending with a cruciform chamber.
This is a shot of Kerbstone K15, the 'Sundial Stone', possibly a sundial or lunar calendar. Is this the oldest sundial on earth?