Extreme Heat Across Wales Exposes Hidden Archaeological Sites Spanning Millennia

An extended period of extreme heat and drought across Wales has brought to light numerous buried archaeological sites, some hidden for two to three decades. The Royal Commission on the Ancient and Historical Monuments of Wales (RCAHMW) has documented discoveries spanning from prehistoric long barrows to Roman-era structures and First World War training trenches.

Unprecedented Drought Reveals Buried History

Wales has received approximately 5 percent of its typical July rainfall following successive heatwaves and drier-than-usual conditions extending from April through June. The parched landscape has triggered drought conditions in parts of the country and scorched grasslands from coast to coast. These severe dry conditions have made long-buried structures visible as distinctive patterns in vegetation—a phenomenon that would previously occur only once every five to seven years during exceptional drought summers.

The exposed sites appear as "crop marks" and "parchmarks" in dried grass and ripening crops. These marks form because vegetation growing above ancient ditches, foundations, and fortifications can access deeper water reserves and nutrient-rich soil, causing them to remain greener than surrounding parched vegetation. When viewed from the air, these contrasting bands of growth reveal the outlines of structures buried for centuries.

Discoveries Documented Across Multiple Regions

Archaeologist Dr. Toby Driver has been conducting aerial surveys from Haverfordwest and Caernarfon airports throughout June and July, racing to record sites before changing weather conditions erase the visible marks. Among significant findings are a rectangular Neolithic long barrow near Welshpool in Powys, estimated to be approximately 5,000 years old, and previously unrecorded double-ditched farmsteads near Llandysul in Ceredigion dating to the Iron Age or Romano-British period. Additional discoveries include fresh details of Roman buildings at Caerhun Roman fort in Conwy and First World War practice trenches beneath a golf course at Deganwy, also in Conwy.

Dr. Driver noted that challenging wind conditions during aerial surveys made some flights difficult, though many crop marks appear distinctly when viewed from above. In cases where marks are faint due to extreme desiccation, digital image rebalancing techniques help reveal details that might otherwise remain invisible.

A Changing Pattern for Archaeological Practice

The increasing frequency of severe drought conditions means archaeologists can no longer depend on waiting years between major discovery opportunities. What once required patience for rare extreme summers now occurs annually, fundamentally altering how aerial archaeology is planned and conducted. The RCAHMW has released photographs from Dr. Driver's reconnaissance flights, with the national archive for the Welsh historic environment preserving these records for future study and analysis.