An atypically long, hot and dry summer in the U.K. has revealed outlines of ancient archeological sites previously unknown to researchers.

The sites include Iron Age settlements, prehistoric cemeteries, Roman farms and Neolithic monuments dating back thousands of years.

Aerial archeologists, who fly around in search of evidence of ancient structures, have benefited from “perfect conditions,” said Historic England in a news release.

They are on the lookout for patterns etched into crops and grass known as “cropmarks,” which form much more readily in hot weather as lush green fields become parched and dry out.

The marks expose the outlines of historic buildings because the grass or crop above them grows differently and has a different colour than the plants in the surrounding soil.

Damian Grady, the aerial reconnaissance manager for Historic England, said in that same release that this has been his busiest summer in two decades of flying.

Archeologists are keen to map the sites so that they can determine how significant they are and how best to protect them.

One of the discoveries that Historic England has described as “exciting” is a pair of mysterious Neolithic cursus monuments they believe date between 3000 and 3600 B.C. They are considered to be one of the oldest types of monuments in England, but archeologists have not yet determined their purpose.

In Yorkshire, a “well-explored” area in the north of the country, archeologists discovered the remnants of Iron Age burial sites sometimes associated with elaborate burials involving chariots.

“It has been very rewarding making discoveries in areas that do not normally reveal cropmarks,” Grady said.