In the 1940s and 1950s, Richard John Copland Atkinson proposed that construction occurred in three phases, which he labelled Stonehenge I, II, IIIa, IIIb, and IIIc. This sequence has recently been revised in Archaeological Report (10) published by English Heritage [ Phase I (2950-2900 BCE) ].
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.
Stonehenge: Eclipse Computer?
Plan of Stonehenge with the Aubrey holes, the Heel Stone, and the Station Stones 91, 92, 93, 94 marked (image from Rodney Castleden The Making of Stonehenge. London and New York: Routledge, 1993. p. 30)
Gerald Hawkins, a Professor of Astronomy, concluded that Stonehenge was a sophisticated astronomical observatory designed to predict eclipses (Stonehenge Decoded). The positioning of the stones provides a wealth of information, as does the choice of the site itself. If you can see the alignment, general relationship, and the use of these stones then you will know the reason for the construction. The author, and other astronomers, discovered the 56-year cycle of eclipses by decoding Stonehenge!
The movement of stones once each year from an initial fixed position allows to predict accurately every important lunar event for hundreds of years. This computer would need resetting about once every 300 years by advancing the stones by one space. Mankind generally used the cycle of the moon as a unit of timekeeping.