The record-breaking hot, dry weather in the United Kingdom might be bad for the region’s crops — and in turn, the formation of crop circles — but the persistent arid conditions that are drying out farmers’ fields are revealing images etched in the landscape of a different kind, called "crop marks". While their man-made origins aren’t nearly as mysterious as the puzzle that the formation of crop circles presents, the marks — shadows of long-lost ancient structures that once inhabited these sites — are offering archaeologists new clues as to where to dig to unearth long-buried secrets.

Crop marks are a fairly subtle occurrence across the UK countryside, caused the difference in the composition of the soil where ancient structures once stood: as it still is today, construction projects throughout history typically required the excavation of at least some part of the building site to accommodate the structure, ranging from simple post-holes for vertical supports to ditches dug around battlements. After the structure itself has disappeared, nature fills the excavations with soil; however, this soil tends to be more fertile, and retains water better than the surrounding soil that hadn’t been disturbed. Centuries later, dry conditions can exaggerate the effect that this more-fertile soil has on the vegetation growing in it, appearing comparatively greener than the parched plants that surround them.

While the hot, dry conditions being experienced by the UK is bad news for most, it has been a boon for archaeologists searching for new dig sites from the air, including aerial archeologist Toby Driver. New ruins have been discovered across Wales, including an unidentified Celtic site near Tywyn, Gwynedd, along with prehistoric settlements and what may be an ancient Roman fortress in Monmouthshire.

"All around Wales we are adding in new bits of history. Right across Wales we have got some stunning discoveries," exclaims Driver, of whom is the Senior Aerial Survey Investigator for the Royal Commission on the Ancient and Historical Monuments of Wales (RCAHMW). "It is a strange and exciting thing to see. It has been an incredible three weeks."

"We have had periods of dry weather in the past, where cropmarks and parching have exposed archaeology, but this current spell is really exceptional both in extent and longevity and the last time it was to this extent was probably back in the 1970s," according to Louise Barker, a senior investigator of archeology with RCAHMW.