Wiltshire, England's favorite prehistoric monument might have just become a little bit less mysterious.

Archaeologists and historians have long been on the fence as to whether Stonehenge was ever a complete circle. The lack of stones on the southwest side gave leverage to the argument that it was purposely left uncompleted. The argument was at a stand-still until recently, when a too-short hose shed some light on the issue.

After a heatwave, stewards began the usual process of watering the grass—but for some reason, last year, their hose wasn't long enough and the water couldn't reach the inner circle. Eventually, thanks to hot weather and lack of water, outlines of two missing stones appeared. "We maintain the grass with watering when it's very dry in the summer, but our hosepipe doesn't reach to the other side of the stone circle," English Heritage's Susan Greaney said. "If we'd had a longer hosepipe we might not have been able to see them."

These outlines were previously undetected even after using methods such as geophysics. When structures are buried in the ground for a long time, it changes the way the grass in an area grows. When the grass dried out, it became apparent that more stones were once present.

"A lot of people assume we've excavated the entire site and everything we're ever going to know about the monument is known," Greany said. "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."