Stonehenge is one of those rare sites on Earth that has always been shrouded in mystery. There are many theories about its purpose, but one particular mystery about its shape could now be solved.

After spotting dry patches at the site, one of the site's keepers realized that the patches might signify where other stones once stood in Stonehenge. If true, this means that the Neolithic structure was once completely round.

Stonehenge, located in Wiltshire, England, is one of the most famous sites of the world. It consists of a ring of standing stones set into the Earth. Archaeologists believe it was built anywhere from 3000 BC to 2000 BC.

The monument has long been a source of mystery. Theories about its purpose range from it serving as a burial ground to serving as a place of healing to being a prehistoric observatory.

However, one mystery interested archaeologists the most: Was Stonehenge once completely round? Most researchers believed that the structure was deliberately left open because they never found proof of stones ever existing where they would enclose the structure as a circle. However, thanks to a recent dry summer in the UK, along with a short hosepipe, those archaeologists could now have an answer.

"I was standing on the public path looking at the grass near the stones and thinking that we needed to find a longer hosepipe to get the parched patches to green up," says Tim Daw, a steward for English Heritage. "A sudden lightbulb moment in my head, and I remembered that the marks were where archaeologists had looked without success for signs that there had been stone holes, and that parch marks can signify them."

Daw immediately alerted archaeologists who are studying the area and looking for photos taken during Stonehenge's past, checking for those dry patches throughout history. If they appear in other images, it suggests that there are stones missing and that the monument was, in fact, once round.

Researchers indicate that this points out how much we still don't know about Stonehenge.

"A lot of people assume we've excavated the entire site and everything we're ever going to know about the monument is known," says Susan Greaney of English Heritage. "But actually there's quite a lot we still don't know and there's quite a lot that can be discovered just through non-excavation methods."