A series of prehistoric carvings was found at the Grange Stone Circle in Lough Gur, County Limerick, Ireland, last month, the Irish government announced in a statement Tuesday. Lighting techniques developed by an archaeological photographer revealed concentric circles and arcs carved along the back and sides of an entrance stone.

Leading Irish archaeological photographer Ken Williams has developed different methods of lighting stones that have allowed him to see more minute details such as the discovered carvings. When he was recently checking on the site, he noticed the presence of concentric circles and arcs along the back and sides of a stone at the north entrance passage of the prehistoric enclosure. These kinds of carvings are extremely rare for the area.

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“The carvings are quite like those at passage tombs in the North and East of the country, such as Knowth and Newgrange, but there is only a single carved stone of this kind in Munster or Connaught,” Elizabeth Shee Twohig, an expert on megalithic and rock art, said in a statement.

“It is possible that the stone is contemporary with the banked enclosure henge at c.3000 BC and was incorporated into the circle built inside the enclosure at a slightly later date,” she continued.

Williams plans to publish his findings in an academic paper, where he will compare the carvings with similar discoveries.

The Grange Stone Circle is the largest standing stone circle in Ireland, with 113 contiguous standing stones set in an almost perfect circle at 150 feet in diameter. The upright stones are backed by a 4-foot-tall and 30-foot-wide earthen bank. Erected ca. 2,200 B.C.E., after the arrival of Bronze Age people, it served as both a ritual site and an astronomical calendar. The largest stone on the site, Rannach Chruim Duibh, weighs more than 40 tons and stands at over 13 feet.

“This is a site that has both captivated and intrigued locals and visitors for many years,” said Malcolm Noonan, Ireland’s minister of state for heritage, in a statement. “It shows yet again the capacity our national monuments have to surprise and engage us.”