Geoffrey of Monmouth, The British History of, translated from the Latin by A. Thompson and J. A. Giles, James Bohn, London, 1842, p.158 (Bk 8, Ch. 11).
I am indebted to Robert Temple for the bulk of the information contained in this post and the majority of the illustrations used appear on his website at http://www.egyptiandawn.info.
The Mzora stone ring is a Neolithic ellipse of 168 surviving stones of the 175 originally believed to have existed. The tallest of these stones is over 5m in height. The ellipse has a major axis of 59.29 metres and a minor axis of 56.18 metres. At the centre of the ring, and quite probably a much later addition, is a large tumulus. Not much remains of this tumulus today, the bulk of the damage to it seems to have been done by excavations undertaken in 1935-6 by César Luis de Montalban. It was he who cut across the mound in two intersecting trenches leaving the distinctive ‘X’ shaped scar visible today (Temple, Robert (2010). Egyptian Dawn. London: Century. p378).
The only survey of the site was conducted in the 1970s by James Watt Mavor, Junior of the Woods Hole Oceanographic Institute in Massachusetts, USA. It is this survey that revealed Mzora to be not only remarkable in its own right but to have implications for the history of megalithic sites in Britain.
“The remarkable thing is that the largest, the 12, 35, 37, was known and exploited more than any other with the exception of the 3, 4, 5.”
Thom, Alexander (1967). Megalithic Sites in Britain. Oxford: OUP. p.27.
“If a ‘megalithic yard’ of 0.836 metres … [is used] … then the major axis and the perimeter of the ring take on values nearly integral.”
Temple, Robert (2010). Egyptian Dawn. London: Century. p379.
Thom proposed that achieving a circumference measured in whole numbers was of paramount importance to the builders of megalithic rings:
“When Megalithic man set out a circle with a diameter of 8 units he found the circumference very nearly 25 units but in general he could not get nice whole numbers like these for both the diameter and the circumference simultaneously. Probably the attraction of the ellipse, and we know of over 30 set out by these people, was that it […] was easier to get the circumference near to some desired value.”
Thom, Alexander (1967). Megalithic Sites in Britain. Oxford: OUP. p.31.
But there are further wonders.
According to the diagram below by James Watt Mavor the following astronomical phenomena are marked by the circle:
Stone 30 marks the summer solstice sunrise.
Stone 146 marks the summer solstice sunset.
Stones 61 and 62 mark the winter solstice sunrise.
Stone 118 marks the winter solstice sunset.
Stone 47 marks the equinoctial sunrise
Stone 132 marks the equinoctial sunset
Temple, Robert (2010). Egyptian Dawn. London: Century. p391.
For further discussion of the importance of this site see Chapter 8 of Robert Temple's book, Egyptian Dawn (2010).
NOTE: This isn't the only stone circle in Africa to share its construction methodology with British sites. The Nabta Playa stone ring in Southern Egypt conforms to Alexander Thom's "Type I egg" geometry. The mystery deepens ....
EDIT: I've created some rough illustrations below in Photoshop to compare the James Watt Mavor survey with the Google Earth images from my previous post.
Caveat: unless the camera taking the photograph for Google Earth is directly overhead the object of interest, the image will be slightly distorted and therefore an exact match with the survey is not possible. Nevertheless as a rough guide to the features and orientation of the site the images match up surprisingly closely.