One of the many mysteries of Stonehenge may have been solved, not because of a scientific breakthrough or painstaking research, but after a maintenance team’s hosepipe turned out to be a little short.

Archaeologists have long argued over whether the ancient monument was once a perfect circle or if it was always, as it is now, an incomplete ring.

When a hosepipe used to keep the grass green in hot spells failed to reach a broken part of the circle, unsightly brown patches began to appear. Custodian Tim Daw was fretting over the blemishes when he realised they matched the spots where stones would probably have stood if the monument had been a complete circle.

Daw said it was a “lightbulb moment”. “I was standing on the public path looking at the grass near the stones and thinking we needed to find a longer hosepipe to get the parched patches to green up,” he said.

“I remembered that the marks were where archaeologists had looked without success for signs that there had been stone holes. I called my colleague over and he saw them and realised their possible significance as well. Not being archaeologists, we called in the professionals.

“I am still amazed, and very pleased, that simply looking at something that tens of thousands of people had unwittingly seen, can reveal secrets that sophisticated machinery can’t.”

The professionals duly took charge. Aerial photographs were hurriedly commissioned before the rain could come and remove the brown patches, and the scorch marks on the western side of the Wiltshire site were mapped, and some of the brown patches indeed tallied with where stones would have stood if the circle were complete.

Other brown patches corresponded to recorded archaeological excavations, included trenches dug by the engineer William Gowland in 1901. That some of the patches matched the site of the trenches supports the theory that they indicate disturbed ground.

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