Stories that stuck
Myths
Merlin
Geoffrey of Monmouth, in his History of the Kings of Britain in 1136, explained the idea that the wizard Merlin built Stonehenge: an idea that, English Heritage notes, was widely accepted until as late as the 16th century.1
Druids
John Aubrey in the 17th century and William Stukeley in the 18th century both believed the structure to be a Druid temple. This idea has been rejected by more-recent scholars, as Stonehenge is now understood to have predated by some 2,000 years the Druids recorded by Julius Caesar.2 Whether it was used by the Druids (Celtic priests) is doubtful, but present-day Druids gather there every year to hail the midsummer sunrise.2
The Slaughter Stone sometimes has a reddish colour because rainwater reacts with the iron it contains. English Heritage says this may explain its name, given by Victorian visitors who imagined that Druids had practiced sacrifices here.3
A prehistoric computer
In 1963 American astronomer Gerald Hawkins proposed that Stonehenge had been constructed as a "computer" to predict lunar and solar eclipses. Most of these speculations, too, have been rejected by experts.2
A place of healing
In 2008 Tim Darvill and Geoffrey Wainwright suggested that Stonehenge was used in prehistory as a place of healing. However, analysis of human remains from around and within the monument shows no difference from other parts of Britain in terms of the population's health.2
Aliens
Stonehenge was not built by aliens. The claim gained popularity by way of the book Chariots of the Gods?, published in 1968, by Erich von Daniken. Britannica says von Daniken's claims and others like them have been debunked by scientists and other researchers.2
A settled Welsh origin for the Altar Stone
That is no longer something this site will state as settled. English Heritage's building page still names south-east Wales; a 2024 Nature study, summarised by UCL, names north-east Scotland. The full note is with the stones.