Researchers have long investigated each part of the monument -- the massive central trilithons, the smaller bluestone settings, the sarsen circle capped by lintels, the outer bank and ditch -- debating whether the outer prehistoric stones were once completely round.
Indeed, the possibility that Stonehenge was an intentionally incomplete monument, with the sarsen circle only finished on the north-eastern side, has been suggested since the mid 18th century.
Now, a hosepipe too short to cover the outer part of the circle where no stones still stand, may have provided a definitive answer, revealing what excavations and high-resolution geophysical surveys failed to find.
Spotted by Daw, 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.
Buried or once-buried structures interfere with plant growth and develop at a different rate to those growing immediately adjacent. In this case, deep stone holes may have changed the earth permeability, affecting the grass growth.