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An exceptionally dry summer — and a watering hose that was too short — helped archaeologists clear up a centuries-old mystery surrounding Britain's Stonehenge monument: Did the ancient stones make a complete circle in ancient times?

The dried-up grass around Stonehenge suggests that they did. A steward at the site, Tim Daw, noticed in July 2013 that there were some particularly parched spots on the monument's southwest side, spanning a gap in today's incomplete arc of stones. Archaeologists say those spots represent places where the ground was disturbed by the digging of stone holes.

"If these stone holes actually held upright stones, then we've got a complete circle," Susan Greaney, senior properties historian for English Heritage, said in an emailed statement. "It's really significant, and it shows us just how much we still have to learn about Stonehenge."

A diagram of Stonehenge pinpoints the locations of stones and chalk pits known as "Aubrey holes," as well as parched areas where stones might have once stood. English Heritage / Antiquity

Greaney explained to the BBC that the grass at Stonehenge is watered during dry spells in the summer, "but our hosepipe doesn't reach to the other side of the stone circle."

"If we'd had a longer hosepipe, we might not have been able to see them," she said.

The phenomenon was first reported a year ago by British archaeologist Mike Pitts, and explained in detail in September's issue of the journal Antiquity.

"This is a wonderful piece of serendipitous research, highly productive and promptly published," Pitts says. "If anyone remained unconvinced that new, targeted excavation at Stonehenge is needed, surely any doubts must now be dispelled?"