Constructed without the use of draft animals and shaped by stone tools, Stonehenge was erected many miles from the quarry from which the stones came. It is an amazing feat of engineering, and many stories, both old ones and retellings, frequently name Merlin as this engineer. This is due largely to one Gerald of Wales (Giraldus Cambrensis), a historian of the 12th century, who wrote a book titled The History and Topography of Ireland.

Gerald called Stonehenge "The Giant's Dance," because he had heard stories that giants brought the stones from Africa to Ireland, and built the monument (by some accounts on Mount Kildare, and by others "at Ophela, near the castle of Nas" (O'Meara, ). Later, Gerald said, Aurelius Ambrosius, king of the Britons, had Merlin bring the stones to Britain.

However, the archaeological evidence at Stonehenge simply does not support an Arthurian date of construction. The archaeology points to a construction date between 5,000 and 3,000 years ago (more than likely, several construction dates over this time). Stonehenge is angled such that on the equinoxes and the solstices, the sun rising over the horizon appears to be perfectly placed between gaps in the megaliths. This is doubtless not an accident, and probably contributed to the stories of its mysterious origins.