The Metrology of the Brochs

by John Neal author of “All Done With Mirrors”

Throughout Scotland and the Scottish islands there are in excess of 200 major broch sites. The following analysis is taken from, what I believe to be, the accurately measured inner diameters of 49 of them as supplied by Professor Euan MacKie. The modules are expressed in English feet although the original measurements were taken in metres and converted to feet at the rate of 3.2808427 feet to the metre. The range of diameters extends from the smallest, at Mousa, 18.897654ft, to the greatest at Oxtrow at 44.816311ft.

The evidence would imply that a professional class of masons were employed in their construction throughout the area of their range and the time span of their unique design. The system of measurement employed in the brochs, both in the module lengths and the methods of application, is identical to that of the preceding megalithic -Neolithic/Bronze Age societies, and to the cultures that succeeded them. The most interesting fact that clearly emerges from the cumulative evidence is that the builders applied certain formulaic procedures in their plans. The vast majority of the diameters are multiples of seven in terms of the various feet that are used; and these diameters become exactly seven when known multiples of these feet are employed. For example, diameters that are 21 feet would be seven yards (ancient metrologists sometimes expressed the yard as a double 1½ ft cubit); if they are 28 feet they are seven double two-feet cubits; at 35 feet they are seven five-feet paces (double step) and at 42 feet are seven fathoms.

As the size of the brochs increase, the numbers of the modules do not; the module itself increases in order to maintain the numerical formulae. The first six brochs of the list illustrate this point:

Mousa; 18.9ft = 21 Assyrian feet of .9ft.

Nybster is 21 English feet.

Ousedale Burn; 21.84756ft = 21 common Greek feet.

Castle Cole; 22.176ft = 21 Persian feet of 1.056ft.

Armadale Burn; 22.94ft = 21 Belgic feet

Dun Carloway; 24ft = 21 royal Egyptian feet of 1.142857ft.

The following 20 brochs, with a couple of notable exceptions, from number 7 in the list, Kiess North, at 28.8934ft to number 27, Clachtoll, at 31.36ft, have diameters that are each of 28 feet which range from Iberian to archaic English.

From number 28, Midhowe, to number 31, Loch of Huxter, are each of 35 feet of the Assyrian variants; the diameters of the next three, from 32 to 34, revert to being 28ft of the greater measures, royal Egyptian and Russian. From numbers 36 to 46 the diameters are all of 35ft in terms of the range of possible measures between the lesser Roman values ascending to the greater values of the royal Egyptian. Finally, when the diameters exceed 40 whole English feet, the division of the final three brochs of the list, are in terms of 42 feet of the common Egyptian and the Persian standards.

The dimensions of the brochs with the measured values and the theoretical absolutes are as follows:

This diameter has a clear resolution in terms of the Assyrian Root foot of .9ft at 21 or seven yards.
Obviously seven three-feet yards diameter, perimeter 22 yards or 66ft. Module – English foot.
3Ousedale Burn21.85041268.672725
The module here is the Common Greek “yard”, each three feet of 1.04036ft (Root Geographic) and 22 such yards perimeter or 66 common Greek feet.
4Castle Cole22.17849769.703847
Seven yards of The Persian foot of 1.056ft, (the 5000th part of the Statute mile). Again, 22 such yards or 66ft perimeter. This foot is often encountered in the Gallic 7500 feet leagues.
5Armadale Burn22.96589972.178539
Obviously this diameter is seven “metres”. The metre is composed of three Belgic feet; it is impossible to say if they are Standard Geographic, at 3.284582ft or Root Geographic at 3.277134ft. A plus or minus value on the original measurement would resolve it.
6Dun Carloway24.01576975.47813
One seventh of this diameter (24ft) is three royal Egyptian feet of 1.142857ft.
7Keiss North25.91865781.458637
25.8934ft is 28 feet of the Root Geographic Iberian foot, this is within 1/3 of an inch of the measured length.
8Dunrobin Wood26.37797582.902208
This is eight yards composed of what are termed Sumerian feet of 1.099636ft, yielding a perimeter of 75 Sumerian feet of 1.10592ft, 50 cubits of 1.65888ft or 30 steps of 2.7648ft. This is also the Spanish vara of Burgos, therefore it additionally has a three feet subdivision, so this perimeter could also be viewed as 90 Iberian feet.
The same solution must be forwarded here as that of Dunrobin Wood, whereas the margin of error at that site is around one part in 2000, the margin here would be one part in 800.
10West Burra Firth26.9029184.552003
The most likely solution here is a Roman foot module of .96ft because these feet at 28 to the diameter equal a rational 88 feet perimeter, which is a module number often encountered in the older megalithic monuments. The margin of error is ź inch overall.
This too would have the 28 Roman feet solution, very accurately at 99.983 percent in terms of the Standard Canonical Roman foot of .96768ft.
With less than a quarter inch error on the diameter, this is 28 Standard Geographic common Egyptian feet of .993071ft (6 sevenths of the royal Egyptian foot). Therefore giving the same numerical solutions as the preceding five circles. Many other modules are compatible with this diameter, it is ten Spanish varas as used in California, 25 Sumerian feet and 24 royal Egyptian feet.
It is difficult to see this as anything other than an intended 28 English feet; it is about ½ inch short.
15Dun Troddan28.08401488.264042
The same applies to this circle, in this case it is an inch too long.
This measure is identifiable as a Root Canonical Greek foot of 1.0057142, as identified by Martin Folkes in 1736; he had noted it as being engraved on a Standards Stone at the Roman Capitol. At 28 to the diameter it offers the same numerical interpretation to the previous circles, as do the following.
17Dun a’ Chaolais28.805890.532511
At exactly 28.8 feet this is 28 common Greek feet at Root Classification.
29.4668ft is 28 Standard Persian feet of 1.052386ft.
19Howe of Hoxa29.72443593.419652
This length is about a 10th of an inch short of 28 Root Geographic Persian feet of 1.062034ft.
In this case, the diameter is 28 Root Belgic feet of 1.071428571feet, again with about a tenth of an inch in excess in the measured overall distance.
28 Standard Canonical Belgic of 1.08 feet would be 30.24ft.
24Caisteal Grugaig30.7743096.719243
These three are within a fifth of an inch overall of 28 Standard Sumerian feet (the basis of the Saxon or Northern foot). Additionally, the perimeters would also be 100 Standard Canonical Roman feet of .96768ft.
This is accurately 28 feet of the Standard Canonical Sumerian foot of 1.10592ft, this perimeter taken as 97.32096ft is the precise inner diameter of the Stonehenge Sarsen circle; 100 Standard Geographic Roman feet.
26Dun Fiadhairt31.23362398.162814
This distance at a little over half an inch either way would make it either the Standard or Root Canonical classification of the archaic foot of the “yard and full hand” at 1.11111ft.
This is very clearly 28 of the Standard Canonical classification of the same foot, at 1.12ft.
Were these circles about half inch longer at 31.68ft, when divided by the next multiple of 7 at 35, it equals the Root Canonical value of the Assyrian foot of .905142ft; thereby making the perimeter rational to the same classification of this foot at 110. This number lends itself ideally to the 2½ ft “step” division at 44 in the perimeter.
This circle offers the same numerical solutions in terms of the Root Geographic classification of the Assyrian foot, 35 of which equal 31.861ft.
31Loch of Huxter31.955408100.43128
The Standard Geographic value used in the same way would yield a diameter of 31.9334ft.
33Dun Telve32.283492101.4624
If these diameters are taken as 32.256ft, about one third of an inch short of the measured distance, there would be 28 Standard Canonical royal Egyptian feet of 1.152ft. Interestingly, the perimeter would be exactly 100 Standard Geographic Greek feet of 1.01367ft.
34Achvarasdal Lodge33.070894103.9371
The solution to this circle is 28 feet of the Root Geographic Russian foot which would be equal to 33.04106ft – less than a half inch difference of the measured length.
35Dun Boreraig33.267745104.55577
At a little over an inch too long on the diameter, it is proposed that this is the least accurate circle yet dealt with at around one part 400. The diameter may be 32 Standard Canonical common Greek feet of 1.0368ft, this would yield a perimeter of 100 Standard Geographic common Greek feet of 1.0427245ft. This is the outer diameter of the Stonehenge lintel ring.
This is exactly 440 to 441 35 Root Reciprocal Roman feet at .952381ft.
37Carn Laith33.464596105.17444
35 Root Reciprocal Roman feet, error 1:600 or 1/3 inch.
33.6ft would be about ¾ of an inch short of 35 Root Roman feet. (1:550).
39Dun Osdale33.858297106.41179
This diameter is only about a tenth of an inch short of 35 Roman feet of .96768ft at 33.8688ft. (Standard Canonical).
40Keiss West33.98953106.82424
This length is also at an ideal 33.985 thirty five Roman feet of the Root Geographic .9710ft
This circle is less than ¾ of an inch too long to be exactly 35 Standard Geographic Roman feet of .9732096ft.
42Dun Beag35.367484111.15495
This circle is less than ½ inch short of being 35 Root Geographic Greek feet at 35.4ft.
43Burray East36.08927113.42342
At 36.0818 feet this length is 35 Standard common Greek feet of 1.030909ft, about one tenth of an inch difference on the measured diameter.
44Keiss South38.320243120.43505
There are two possible interpretations of this length; it could be 35 feet diameter of the root Sumerian foot of 1.097142ft, in which case it would be an error of slightly under an inch at 38.4ft. Alternatively at the same length, it could be 28 cubits of the Iberian Root value or 14 varas.
At 39.3346ft, about 1/3 of an inch difference, it is equal to 35 feet of the Root Geographic archaic English yard and full hand.
Almost exactly, at 40.22857ft, there would be 35 Root Canonical royal Egyptian feet.
At 41.709ft this diameter would be 42 common Egyptian feet of .993071ft. It is also 40 common Greek feet of 1.04272ft. The former is the more likely interpretation, as the length would be 28 cubits or 7 fathoms of this foot.
48Dun Ardtreck44.488227139.82014
This measurement is taken from the surviving semi-circle. At 44.4528ft, within less than ½ inch of the measured length, this is exactly 42 Standard Canonical Persian feet of 1.0564ft. This offers the same numerical interpretation as Tirefuar.
At the value of an extended Persian foot times 42 at 44.808422 – this is less than 1/10th of an inch from the measured value; it offers the same numerical solution.

At the value of an extended Persian foot times 42 at 44.808422 – this is less than 1/10th of an inch from the measured value; it offers the same numerical solution.

Although the above interpretations of the broch dimensions are the simplest, therefore the most likely solutions, within such a tightly related organisation of measure alternative resolutions are possible. Site 1, Mousa for example, although this broch is seven “yards” in terms of the Assyrian foot it may also be viewed as seven steps, the 2½ ft module, whose detection in megalithic monuments gave rise to the belief in the “Megalithic Yard”. At Mousa the step would be 2.5 Belgic feet of 1.08ft, therefore 2.7ft. Other values of this Belgic foot as well as variants of the Sumerian feet would yield a range of measures acceptably close to the hypothesised 2.72ft Megalithic Yard. For reasons that have become obvious, it is folly to attempt to define such a module as a habitually employed element of the megalith builders. If the seven division of no. 7, Keiss North, is relinquished for a division by eight, it would be eight Belgic yards whose constituent foot is 1.08ft, the perimeter would then be an integer in terms of modules the 175th part longer. This perimeter would then be 25 such yards composed of feet of 1.08617ft; this could also be expressed as 30 steps of 2.715428ft, the measure recently described by Robin Heath as the “Astronomical Megalithic Yard”.

It is also noted that not all of the diameters can be expressed in multiples of seven. Numbers 8,9 and 35 may only be divided by multiples of eight. It is unclear why the seven counting base for diameters is sometimes abandoned; but it is often encountered in ancient metrology. Perhaps there was some compelling reason that a broch or circle had to be exactly a particular size, leaving but small choice as to the module.

There is also a distinct possibility that certain canonical lengths should be expressed in the constructions. Echoes of a far older metrological discipline are perpetuated in certain of the brochs. I had previously noted that certain lengths seem to be equally comfortable when expressed as either a perimeter or a diameter in circular structures. The examples of such occurrences in the brochs are the perimeters of no. 25, Kintradwell and no. 35, Dun Boreraig; they are respectively the inner and outer diameters of the Stonehenge lintel circle. The evidence suggests that such metrological standardizations were common in the Iron Age. One example being the wheel gauge of the chariot recently excavated in Yorkshire; remarkably, at 1.45 metres it is identical to that of the Edinburgh Iron Age chariot burial. This is the lesser value of the five Roman feet “pace”, as found at broch 36, Gurness, the diameter of which would be 7 such five feet paces of the chariot gauge. This particular gauge is found in wheel ruts, whether they have been inadvertently or deliberately cut, throughout the ancient world. Notable examples occur in Pompeii, Malta, Corinth and Persia

Yorkshire Iron Age chariot in situ

Such observations as have been made here concerning the broch dimensions with regard to eliciting the rational sets of numbers, can be equally accurately applied to the older megalithic circles. As indeed they may be applied to interpret later cosmologies, such as the Saxon “King’s Girth” or older biblical metrology such as the dimensions of the Mosaic Tabernacle. The Romans used the same criteria in founding their towns, as did those they supplanted. Recent excavations at Silchester have revealed an Iron Age street grid that is in all respects similar to the imposed Roman, but angled at a 45 degrees slant.

The statement, that the system of measures has been accurately maintained from very remote antiquity until the present day is very easily demonstrated. As the best preserved megalithic ring in Britain is deep within the domain of the brochs, on Orkney, the Ring of Brodgar, it is as good a demonstration of this fact as could be wished for. Alexander Thom gave the diameter as 340.7 + .44ft and stated that this was 125 Megalithic Yards. At 340.90909ft, exactly within the measured range, this would yield a Megalithic Yard of 2.727272 feet (Root Reciprocal); this is the vara as preserved in California and is 175 to 176 to the vara of Castile. At precisely 2.742857ft this is the official standard used by the Spanish bureaucracy until very recent times.

However, if one divides this diameter by seven, a more rational module emerges. One seventh of the Brodgar diameter is seen to be 10 five feet paces whose constituent foot is the Root Reciprocal value of the Common Egyptian foot of .97403ft, the perimeter is consequently 1100 common Egyptian feet or 220 paces. Even more obviously this perimeter, at 1071.428ft is exactly 1000 Root Belgic feet giving a closer pace to the human equivalent of 200 at 5.35714ft. It was the detection of this sort of module that led Alexander Thom to call it the Megalithic Fathom, which he tried to pin down to a constant of 5.44 feet. There is no such constant; each ring must be dealt with individually and its metrological solution sought in the rational numbers that emerge. This was the major oversight that prevented Thom from pinning the system down; the fact that he showed no particular preference for his solutions to be in rational numbers of his proposed module.

The fact of the matter is, that the vast majority of the megalithic rings can be metrologically interpreted by the methods that have been demonstrated on the brochs. All that is necessary is knowledge of ancient metrology, the module lengths and multiples, which is nowadays universally lacking. Sadly, this is a development that has come about in the last half-century, it was not always so. Until the demise of Flinders Petrie the majority of archaeologists had a fair working knowledge of the subject. In the older editions of encyclopaedias such as the 1911 and 1915 editions of Britannica, Petrie wrote very extensive articles on the subject, in which he identified and listed in ascending order, examples of all of the modules discussed here. In modern editions scarcely a paragraph is devoted to the subject.

The broch builders therefore preserved methods and modules that had been used by the megalith builders that predated them by millennia and the same modules survived into the present epoch. Although the instruments of measurement may wear out, the standards by which they manufactured them would be accurately maintained in the dimensions of that which was already built. The conjectural purposes of brochs, as well as being the residences of chieftains, council chambers, courts, temples or redoubts could also have been the Weights and Measures bureau in its very dimensions.

The reason that we can now be certain about claims concerning metrology, is that we are dealing with absolute values. No longer may the subject be regarded as arbitrary nor conjecture be utilised to substantiate hypotheses. One very good example of the solidity of the theory is the regularity with which the Assyrian variants occur in all cultures. Oppert positively identified the Root value of .9 English feet from measurements of the ruins of Khorsabad. The value of the 175th part longer at .904514ft is exactly given by the copper bar of Nippur, at four feet long it is reported as 1.1035 metres and four times .904514ft is 1.103549 metres. At the next value in the series, the 175th part longer again, it is exactly the 360th part of the outer perimeter of the Stonehenge lintel ring. This particular value was precisely given by Stecchini taken from the diameter of the Grave Circle at Mycenae. These and other values of the Assyrian foot are also referred to as Oscan, Italic and Mycenaean. It therefore comes as no surprise to find it so prominently in the broch dimensions at Mousa, Midhowe, Borrowstone, Yarrows and Loch of Huxter at exactly these values. Equally strong evidence is extant for each of the other proposed measurements.

Although Livio Stecchini, who has sadly died in recent years, was the most renowned metrologist of his generation he missed the fact that the choice of module must be sought in the sensible ratios and rational numbers. When he identified the Mycenaen foot from the grave circle of Mycenae he measured the diameter as exactly 100 feet of what I have termed the Assyrian foot at its Root Geographic classification of .910315ft. It has been my experience that when such an unsatisfactory number as is this decimal as a diameter, an alternative should be sought. If the distance is divided by seven it is 13.0045ft, this is exactly the 12 feet pertica of the Belgic foot of 1.083708ft. There is little doubt that we are looking at identical construction techniques and formulae over a vast geographic area and span of time.

Few examples of measuring instruments survived in Europe, and no ancient plans or diagrams remain; but it is obvious from the similarity of the broch designs that such detailed plans must have been used. It is to Egypt that we must look for pictorial confirmation of the facts regarding metrology as presented here. An abundance of measuring rods are extant and analyses of the dimensions of ancient buildings in very good condition may be used to confirm many modules. Many working drawings may also be consulted, a good example of which is set out below.

British Museum, wooden board overlaid with gesso. Egypt-5601

The human form is always depicted to canonical proportions. The reason that the drawing above is so interesting is that a whole variety of cubits are portrayed. This is proof that an amalgam of modules was deployed in a single creation. If the grid is terms of the four-digit hand, and the cubit is taken as Root at 1.714285ft then the median of the cubits on the left would be this Royal Egyptian cubit. The one above would be two Roman feet at the precise value found at broch 36, Gurness, and the one below would be the Sumerian cubit of 1.645714ft, exactly 24 to 25 of the Royal Egyptian. Only one cubit may positively measured on the right hand side, and it is a complete curler. For if the seated figure were erect, then he would 3 2/3 royal cubits high which would be four of these cubits. In terms of the English foot his overall height would be twice pi, or 6.285714ft, and the basic foot one third of pi. It is not a measure that I am aware of, but has been encountered; I hesitate to offer an explanation feeling that I may be getting out of my depth trying to decipher Egyptian mysteries.

Many more of their techniques may be extrapolated from this drawing, but the object here is to illustrate that several quite separate modules were in contemporary use in a single culture. Wherever one researches ancient measurement one finds the same modules and all of them are founded on such anthropomorphic bases. There is nothing absurd or even unexpected in finding the identical system used in Scotland, after all, the modules are identical, the Root royal cubit used above would fit exactly 625 times into the perimeter of the Ring of Brodgar.

Virtually every aspect of this amazing and elegant system, particularly with respect to the module identification, would be totally obscured by being expressed in the metric system. As the traditional units such as the English foot are being inexorably phased out, we may confidently say that this knowledge has therefore been rescued in the nick of time. Only somebody who habitually thinks in terms of the English foot could have deciphered it. This is because each number that one is confronted with will have a close solution in terms of the English foot. For example, the length of the mean geographic degree according to ancient metrology is 364953.6 feet, the closest round sensible number to this is 360000, when this degree is divided by this number the result is 1.01376 which is the value of the Standard Geographic Greek foot. Metrological analysis really is this simple.

All cultures used all the measures. Does the system as a whole, which all civilizations used as reference, therefore predate all of them? Because one cannot conjecture that there were any direct cultural contacts between the disparate peoples who used the identical system. Indeed, people who have not previously been regarded as civilized in the literal sense, manifestly utilised this sophisticated measurement system to extraordinary degrees of accuracy. But so thoroughly have assumptions over the centuries become orthodoxies, that the truth when it arises is often regarded as preposterous.

this study in revised form is now available in item 5 below, with an introduction to ancient metrology.

  1. Berriman, A. E. Historical Metrology. London: J. M. Dent and Sons, 1953.
  2. Heath, Robin, and John Michell. Lost Science of Measuring the Earth: Discovering the Sacred Geometry of the Ancients. Kempton, Ill.: Adventures Unlimited Press, 2006. Reprint edition of The Measure of Albion.
  3. Michell, John. Ancient Metrology. Bristol, England: Pentacle Press, 1981.
  4. Neal, John. All Done with Mirrors. London: Secret Academy, 2000.
  5. —-. Ancient Metrology. Vol. 1, A Numerical Code—Metrological Continuity in Neolithic, Bronze, and Iron Age Europe. Glastonbury, England: Squeeze, 2016 – read 1.6 Pi and the World.
  6. —-. Ancient Metrology. Vol. 2, The Geographic Correlation—Arabian, Egyptian, and Chinese Metrology. Glastonbury, England: Squeeze, 2017.
  7. Petri, W. M. Flinders. Inductive Metrology. 1877. Reprint, Cambridge: Cambridge University Press, 2013.