A drone flight and a lingering dry spell have exposed a previously unknown monument in Ireland's Boyne Valley, forgotten for thousands of years and long covered by crops — which, struggling to cope with a lengthy drought, finally revealed the ancient footprint. 

Photographer and author Anthony Murphy discovered the site. He was flying a drone near Newgrange, a famous prehistoric stone monument in County Meath, on Tuesday, taking pictures of the known archaeological attractions. Then he saw something strange — a perfect circle, etched in the color of the crops, in an otherwise unremarkable field.

Murphy runs the website Mythical Ireland (also the name of his latest book), which focuses on the megalithic monuments of the Boyne Valley. He knew the local sites well — every passage tomb, every banked enclosure, every archaeological dig. And he'd been flying drones here for months.

He'd never seen this.