Silbury Hill: Metrological Key to the Model of the Earth between Stonehenge & Avebury

Archived: 11 August 2012

The exact location of Silbury Hill is as mysterious as the purpose of the Hill itself, a thirty degree cone, only recently with a flat top, overlooking Avebury and the surrounding hills. The Hill figures in John Michell’s model of the Earth between Stonehenge and Avebury in which one quarter of a degree of latitude, between the two henges, appears to have been measured by a type of Persian foot so as to make the number of feet, in between, equal numerically to that required to perfectly model the Earth using 864:866:867 double triangle.

The double triangle model of the size of the Earth between Stonehenge and Avebury

There are 86400 Persian feet of 1.056 feet (south to north) between Stonehenge and Avebury Ridgeway enabling the Avebury henge to be 86600 of these Persian feet from Stonehenge, then to represent the Mean Earth radius (see Initial Article – missing link). The Avebury henge appears to have been specifically tied to the distinct Latitude of 360/7 degrees.

Figure 1 Avebury Henge and Silbury Hill under snow. Avebury terminates a model of the mean earth radius from Stonehenge whilst the equatorial radius, in the same model, passes through Silbury Hill; so as to give the relation of the quarter degree length to the polar radius. 

In a hand written note in 2004, John Michell had found the distance from Stonehenge to the base of Silbury Hill to be 86400 plain old English feet. In an earlier note to my brother, John stated another interesting fact, that, by his reckoning, Silbury Hill marked a distance from Stonehenge that was 1/240th of the Earth’s polar radius, thus connecting the Hill with the Polar radius despite it punctuating the end portion of the Equatorial length of 86700 Persian feet from Stonehenge to 360/7 degree latitude (the length representing the equatorial radius within the double triangular model.) 

In reaching the base of Silbury Hill from Stonehenge with 86400 feet, John Michell had the same number as that found in the quarter degree of latitude measured in Persian feet of 1.05 feet. This length of 86400, in either unit, numerically relates to the 864 side of the double triangular model and this implies a connection between Silbury Hill and the quarter degree length between Stonehenge and Avebury. 

One 240th of the polar radius is 86893.714285 feet, and this exceeds 86400 feet by exactly 176/175, one of the grid ratios employed for metrological variations, within the ancient world and presumably, therefore, in the megalithic world in which metrological work was first invented. The same portion of the polar radius divides into the 86400 Persian foot length of the quarter degree as exactly 21/20. This reveals why the quarter degree between Stonehenge and Avebury is only 86400 when using the root canonical Persian foot whose formula is 1.056 = 21/20 times 176/175. The builders are giving us a lesson in metrology, that the polar radius of the model is related to the 1/240th part of the polar radius as 21/20 whilst the english foot is related to this as 176/175 so that the correct foot for the model, to measure the quarter degree as 86400 units, is the root canonical Persian foot of 1.056 feet.

Figure 2 Silbury Hill can be studied to reasonable geodetic and metrological accuracy, finding that 86400 feet reaches its southern perimeter and one 240th of the polar radius (both from Stonehenge) reaches its northern perimeter. A line 494 feet long, one 175th of 86400 feet, is shown indicating this as a credible diameter for whatever was initially built or excavated where Silbury Hill now stands  (see also figure 3).

When these two points, 86400 feet and 1/240th of the polar radius from Stonehenge are projected onto Google Earth, the result corresponds as accurately as one could expect to 86400 feet reaching the base of Silbury Hill whilst 1/240th of the polar radius requires an additional length about equal to the width of the Hill itself.

The 864:866:867 model enabled land-based estimation of two of the important circumferences that define the Earth, its equatorial and its mean circumferences, both of these being accessible at the 51 to 52 degree of latitude; through the length of a known angle of Longitude east-west and the length of the north-south quarter degree of Latitude. The two radii for these circumferences will be in the same proportion as the circumferences and by re-purposing the quarter degree’s 86400 Persian feet as standing for the polar radius, the mean radius could be put into a length 200 Persian feet longer and the equatorial radius 100 Persian feet longer still, both these as hypotenuse to the polar radius. Note: as mentioned previously, (found 86 – coming soon) there is always a 2:1 difference between these three radii in a rotating gravitational ball.

GE SilburyInfo
Figure 3 Silbury Hill from a public information board, showing a carved ditch (as seen at Stonehenge and Avebury) which, using the given scale in feet, indicates that the inside diameter was the 175th part of 86400 feet which is 494 feet.

Silbury Hill may have had many uses, but its location enabled the new model of the earth to relate the actual polar radius with its modelled length of 86400 Persian feet. The designed width of the Hill would then be one 175th of 86400 feet which equals 3456/7 (494) feet, 432 royal feet of 8/7 feet and 180 megalithic yards of 96/35 feet. This is nearly 60 feet less than John Michell’s estimate for the diameter of the Hill, 552.96 feet but Figure 1 shows how variable base diameters include 494 English feet. But the hill was built over time and probably more after the model of the Earth and hence Stonehenge was established (around 3000 BCE at the earliest, see

Dating the Hill: Atkinson reported the C 14 date for the base layer of turf and decayed material indicated a corrected date for the commencement of Silbury was close to 2750 BC. An antler fragment, used to cut into chalk, produced a reliable radiocarbon date of c. 2490-2340 BC, for the second mound to the Late Neolithic (whilst not contradicting the 2750 BC date for the initial construction). see

Silbury Hill was built over time and what we see today is unlikely to be what was there during any building of a landscape model of the Earth. However,

  1. Silbury Hill lies on the 864:866:867 double triangle’s 867 length and is the only (surviving) marker for this alignment and length.
  2. It is also true that a length 86400 feet long arrives at its southern base from Stonehenge and that
  3. 1/240th of the polar radius is one 175th part greater and then approximates to the present diameter of the base, that can equally be called octagonal and not circular.

Since it has been a megalithic habit to bury stone monuments in a tumulus then perhaps whatever was once placed there has been superceded and made more indelible for whilst standing stones are often removed once they are in an agricultural setting, large tumulii and indeed pyramids tend to have survived since merely quarrying them consumes too much effort. The establishing of Silbury was probably via the inner size of the ditch that surrounds it, as that would be able to hold an exact measurement. Later silt infills would leave the chalk rim.

Lastly, this is a megalithic answer to the question as to why the root canonical Persian foot should, in particular, divide up the quarter degree to also then have a relationship to the polar radius, that survives through Silbury Hill’s location. John Michell’s notion of this model has been strengthened by the 864:866:867 model, numerical best suited to the Earth’s dimensions, being perfectly commensurate and numerically adapted to the quarter degree of latitude between Stonehenge and Avebury, as if it was intended to be so.

Figure 4 (figure 10.3) The principle divisions of the Stonehenge – Avebury line.

Figure 10.3 of The Measure of Albion shows John Michell getting even closer to the explicit relationship that 86400 English feet times 21/20 times 176/175 equals the 86400 root canonical (R C) Persian feet of the Quarter Degree on The Stonehenge-Avebury line. John studied the itinerary between the Ridgeway and Stonehenge and found a symmetrical pattern puntuated by elements both ancient and modern, marked by “spots” along a road and the limits of Casterley Camp. The middle section is 14,400 feet and the north and south of the interruptions are distances of 36,000 so that, without interruptions, the distance is 86400 english feet.

This means that the interruptions must add up to the excess or difference between 86400 R C Persian feet and 86400 English feet which equals 4838.4 feet. He ends,

“The correspondences between the northern and southern halves of this line, making each a reflection of the other, suggests first of all a musical notation. Musicologists can recognize the intervals and also the numbers involved, such as the octave 864: 1728 that Ernest McClain identifies in his works on ancient musical theory. [RH: see Harmonic Explorer] At the same time, there are other likely interpretations, each involving number and measure.”

The primary reference for this is The Measure of Albion, Robin Heath and John Michell, Bluestone Press, Wales, 2004, p107 now reprinted in facsimile as this book

You can also discover more about this in my Sacred Number and the Lords of Time, pub: 2018.