A mystery 5,000 years old has been solved - because a hosepipe was too short.
Historians have long debated if the outer prehistoric stones of Stonehenge were at one time completely round - but countless archaeologists have failed to find any evidence.
This millienia-old puzzle was solved over the summer because a hosepipe used to water the area simply wasn't long enough.
Every summer stewards at the ancient monument water the site to keep the grass healthy and green and the earth well nourished.
But this year the hosepipe was too short to reach the outer part of the circle - where no stones still stand.
The dried out land revealed marks of parched grass which were spotted by an eagle-eyed volunteer who alerted experts.
English Heritage now reckon the discovery has finally revealed the location of missing sarsen stones which would have once completed the Neolithic circle. Susan Greaney, from English Heritage, said:
Historians have long wondered whether Stonehenge was an intentionally-incomplete circle, but countless high resolution geophysical surveys and excavations have failed to give the answer.
Staff only water the site during the driest weeks of summer, but the hosepipe doesn't reach to the south-west quadrant where there is a gap in the circle.
Worker Tim Daw spotted the patches on the ground - now thought to be 'stone holes' - where the grass was more parched.
He said: "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.
"A sudden light-bulb 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.
"I called my colleague over and he saw them and realised their possible significance as well. Not being archaeologists we called in the professionals to evaluate them.
"I am still amazed and very pleased that simply really looking at something, that tens of thousands of people had unwittingly seen, can reveal secrets that sophisticated machinery can't."