The country is in the grip of a lengthy drought–it's the longest sustained dry spell since 1976–and crops are struggling up and down the Emerald Isle. The effects of the sustained heat and lack of water are apparent in the Boyne Valley, which contains Newgrange, a well-known prehistoric stone monument. A local photographer flying a drone over the area saw, emerging as if by magic, an otherwise unknown pair of concentric circles. The wider area is already a UNESCO World Heritage Site, home to other henges and other monuments. This particular henge had long been covered by the land, with many generations of farmers planting crops directly on top.

The henge dates to Neolithic times, about 4,500 years ago, archaeologists said. The henge would have been a circle of massive wooden posts, all of which have rotted away but have left an organic "footprint," which the photographer, Anthony Murphy, discovered on his recent drone flight. He had flown over the area many dozens of times and had never seen the henge before.

Archaeologists are planning further investigations.