London: Archaeologists have solved one of the many mysteries of Stonehenge, showing that the iconic monument was once a complete circle.
The dry weather in the summer of 2013 at the monument in Wiltshire, close to Salisbury, showed marks of parched grass in an area that had not been watered.
The patchmarks represent the position of the missing sarsen stones which once completed the Neolithic circle, said researchers.
Historians have long wondered whether Stonehenge was an intentionally-incomplete monument, with the sarsen circle only finished on the north-eastern side.
Now, a hosepipe too short to cover the outer part of the circle where no stones still stand, may have provided a definitive answer, 'Discovery News' reported.
Spotted by English Heritage steward Tim Daw and colleagues, the patches on the ground - believed to be "stone holes" - appeared in the sarsen circle exactly where stones were expected to stand.
Such crop marks are produced when plants grow over features that have been buried in the ground for a long time, even long after they have been removed.
English Heritage hopes to corroborate the findings with searching historic aerial photographs of the site and with future observation of the same phenomenon in similar weather conditions.
The details of the discovery were published in the journal Antiquity.