A mid-14th-century manuscript illustration showing Merlin building Stonehenge, an idea widely accepted until as late as the 16th century
© British Library Board (Egerton MS 3028 fol 30)
The earliest surviving written references to Stonehenge date from the medieval period, and from the 14th century onwards there are increasing references to Stonehenge and drawings and paintings of it. At this time, Stonehenge was thought to have been built by the Romans.
During the 12th century, Geoffrey of Monmouth suggested that Stonehenge was built by none other than Merlin, under instructions from King Aurelius, Arthur's uncle, as a burial ground for a group of British nobles slaughtered by Saxons.
"If you are desirous," said Merlin, "to honour the burying-place of these men with an everlasting monument, send for the Giant's Dance, which is in Killaraus, a mountain in Ireland. For there is a structure of stones there, which none of this age could raise, wthout a profound knowledge of the mechanical arts. They are stones of a vast magnitude and wonderful quality; and if they can be placed here, as they are there, round this spot of ground, they will stand forever.
This was an idea which gained popularity alongside much of Monmouth's writings.
Aurelius ordered Merlin to erect round the burial-place the stones which he had brought from Ireland. Merlin obeyed the King's orders and put the stones up in a circle round the sepulchre, in exactly the same way as they had been arranged on Mount Killaraus in Ireland...
You can also read the Legend of the Heel Stone here.