A True Line : an exploration in making and using the tools of the Architectus

An Arts and Sciences entry for the Dragons Laire Candlemas 2021

Arts and Sciences entry.

A True Line : an exploration in making and using the tools of the Architectus

I started my journey towards developing the tools of a Roman architectus or military engineer with building my first Scorpioballista. I started the deep dive into building my own tools with which to make artillery and other equipment. I had for a Time shied away from the fine-tune work that is necessary for building scientific instruments. My first foray into developing scientific instruments I built a small number of things that would be considered the basic surveying toolkit. A groma, a libella, and a measuring stave. A libella, being a relatively simple Carpenter’s square, and the measuring stave were pretty straightforward. these tools however made it possible to start measuring everything I did using Roman units and explore at depth the writings of Vitruvius and others who were quite keen that all objects in the world had their proper ratios.

The Romans were well known for the precision of their measurements both in small features and over great distances. The same minds that built The Parthenon, thousands of miles of aqueducts, and over a million miles worth of roads, managed to build features that in many cases have lasted significantly intact up to today.

so I started the quest of finding out and figuring out how they went about doing that. The next scientific tool I made was the one most alluded to when it came to providing the standard for distance measure. The groma is an upright stave often with a spike to drive it into the ground, topped by a short angled arm which allowed for a pair of perpendicular beams, suspending plumb lines and bobs from each end. Most writers and commentators at the time placed a near religious significance of this tools capability.

Near religious, as it stands, maybe the operative word. From my own explorations I quickly found the groma to be a finicky beast.  Suspended plum lines danced in even gentle breezes making the kind of measurements that an agrimensor (also known as a groma operator) should be able to manage tough in basic field conditions. The accidental bump of an overzealous assistant or a unaware passerby quickly took the groma off of perfectly vertical lines and further complicated sighting.  Holding the pole still enough without planting it in the ground makes reading the lines impossible. On hard ground or rock, short of having a separate tripod consistently at hand, consistent reproducible measurements become nearly impossible.

For a while I thought I must have been just using it wrong. I know my science but perhaps they had some other way of stilling the groma for a good read that I just did not know about.

I read about waxed strings, wave my own chords and cast my own aerodynamic plumb bob weights, in order to try to get a better measurement. Even with all of that, getting measurements and anything other than perfectly still conditions over soft but not loose soil was still an incredible effort. I started looking and trying to reconcile mile after mile of perfectly straight roads and aqueducts with the infuriating instrument in front of me. After researching more it seemed that there were other tools that quietly did great work on behalf of Roman surveyors and engineers, while the groma got all the praise.  Mounting evidence from both primary sources and others who have made reproductions of the groma started to indicate that the Agrimensors may have largely been ceremonial, an almost priestly group dedicated to the ideal of true measurement, when in actuality a number of other instruments were used to do the real work. 

So what then did the work? this question caused me to explore both objects that were clearly and fully known to have done this work albeit with less fanfare than the groma, as well as a small number of potential specialized instruments, whose full use is still somewhat shrouded in mystery. I settled on the following to build and experiment with: first a Chorobates.

The Chorobates has long been reconstructed based off of much later medieval drawings and wood cuts which may have misinterpreted its actual construction. The woodcuts that led to a number of reconstructions show a very much bench type object with rigid end legs which would have made measurements over uneven ground extremely difficult.  According to Vitruvius a 20-ft long stave made up the primary portion.  The longer The stave the potentiality for more accurate measurements however, also the longer The stave the more likely it would be influenced by outside sources and hard to carry and maneuver about a work site. I have made one at 1/5 the actual size, therefore 4 ft in length. Following the recent reconstructions that place the center of The stave over a pivot and use the two and upright arms as supports and a measuring tool for helping to understand the angle is an entirely viable interpretation of Vitruvius’s description. And as much that I have no interest in spiking the floors of my kitchen or delicate sites at which this might be used and or appreciated I have built a tripod that slides on over the spike allowing the chorobates a wide-ranging stability that my groma did not have.

Second I built a water level, the ancestor of the modern spirit level. Made up of a hollow stave with openings at both ends lined with wax. In as much as that water seeks its own level if The stave is placed on a level surface their water will rise to the same place on both sides. I have developed mine to fit snugly over the top of the Chorobates, or to stand on its own. Lastly I am in the process of developing a functional Roman dioptera. These tools were known to the Romans. Consisting of a sighting tube and one or more methods to determine elevation and direction, these with support of the previous two probably were responsible for the Lions share of what his previously been attributed to the groma. Considering that these three tools have been described individually and separately but have also been seen in different forms of combination, I built my reconstruction to allow each of the three aforementioned tools to a fixed to each other and utilize the same system of support. The dioptera is attached to the upright footstave by pivot that allows for angular measurement. The Chorobates slides on over the top of the diopter citing tube as a replacement for the diopter is directional wheel. A pin is used to align the center of the Chorobates over the dioptera pivot. Alignment lines allow the water level to be placed over the Chorobates. Given that often a Chorobates is considered or described to have a water level built into it, this reproduction fits as well if not better Vitruvius’s description.

In addition to this combination tool, I have built two items that are by their nature more speculative. The first is what is known as a surveyor’s square. Only two such devices dated to the second and third century CE in Roman contacts have ever been found. At this time only one remains, and given further information, the one that remains may have been the weaker tool. The better tool unfortunately was lost during world war II during bombing in Koblenz, Germany. Accurate pictures with good diagramming were made and distributed and it is from these that I built my copy. Given the cross-section diagram I believe the original may have had bronze over wood, but if the original was purely bronze it’s thickness would have made It excessively heavy.do I made some point in time at additional bronze fittings, I believe that this reproduction is closer in both cross-section and size to the original. Given how obscure and rare these finds were, this reproduction may be the only one currently existing on this planet.

obviously the speculation in this case is that the Romans likely had more of these that have unfortunately not survived but their use is reasonably clear as these tools are extremely similar to ones used less than 150 years ago.

My second speculative entry is not as rare, with I believe 80 plus finds, however it has been subject to wild conjecture over many years. It is my belief based now off of application and use that the Roman dodecahedron is in fact a multi-use tool for finding level, horizon, and vertical an adverse or hilly conditions, and can be used to help sight constellations for nocturnal navigation and time keeping. In as much as that all of the in situ finds of Roman dodecahedrons that weren’t directly found with a horde of coins, were found in the mountainous regions of lower Germania. These objects were often found containing some measure of Wax which would be explained by the use of candles to find true vertical and therefore to be able to artificially determine a horizon in that kind of terrain. The high cost and skill of their construction, and the variable nature of hole size and even hole presence from one to the next tend to discount the thought that this was a tool with which to knit gloves, nor was it likely a tool to determine the veracity of coinage. This leaves us with the concept of coincident range finding as it’s most likely additional use. Further finds of other Roman dodecahedrons that have been marked with the constellations of the zodiac also speak to the likelihood of stellar measurements for timekeeping and navigation as a plausible use.


Although much of the initial shaping was done using modern tools in order to expedite the process, the measurements that informed The cutting relied largely on my Roman measuring stave. Finishing with largely accomplished with period tools-hand saws to flush cut dowling work,  chisels employed to clean and dress lines, hand and Stone sanding where applicable. Largely made of oak and walnut, some fittings were made of maple or poplar for the sake of having a light clear surface to mark and scribe. In order to more accurately test the capabilities of the instruments, the diopter plates were laser inscribed copies of Roman originals (in the case of the zodiac wheel the timing wheel, and the wheel of the winds. The remaining wheels were designed to keep with the aesthetic and known mathematics of  Imperial Rome 1st-3rd CE

A quick note on the use of the Roman numeral clock face; The same reason that even modern clocks using Roman numerals often note four as IIII as opposed to IV harkens to the early imperial when this was a standard practice, and IV was not used until relatively late in the second century CE.

Use: The methods of use of each tool is specific. Below are example diagrams and pictures Illustrating the proper use and practices.



Surhone, Lambert M., et al. Roman Military Engineering. VDM Publishing, Jun 18, 2010.

Evans, Edith. “Military Architects and Building Design in Roman Britain.” Britannia, vol. 25, 1994, pp. 143–164. JSTOR, www.jstor.org/stable/526994. Accessed 6 Jan. 2021.

Gildart, Charles R. “The Roman Military Road System.” The Military Engineer, vol. 21, no. 117, 1929, pp. 256–258. JSTOR, www.jstor.org/stable/44573117. Accessed 6 Jan. 2021.

Wake, T., “The Roman Army After Marius’ Reforms,” http:// romans.etrusia.co.uk

/roman_army_intro.php, 28 February 2006.

Hayes, Jeff.  Facts and Details .com “Ancient Roman Infrastructure”.  Updated 2018 http://factsanddetails.com/world/cat56/sub408/item2053.html

O.A.W. Dilke (1971): Roman Land Surveyors

I. Moreno (2004): Roman Surveying (from the Spanish Traianus website)


GFW Hauck, RA Novak – Journal of Hydraulic Engineering, 1988 – ascelibrary.org

The Making of Constantinople: Constantine’s “New Rome”


By Kenneth W. Harl, Ph.D., Tulane University

Michael Grant, History of Rome (New York: Charles Scribner, 1978), 52, 264

8 thoughts on “A True Line : an exploration in making and using the tools of the Architectus”

  1. Aelianora de Wyntringham

    This is wonderful! Great work. I loved your video presentations. Very, very nice.

  2. This was an amazing presentation. So much detail and research went into this! I find it fascinating that many of our current surveying instruments aren’t that much different than what the Roman’s used. I especially enjoyed hearing about the various ideas of what the dodecahedron was used for. Excellent craftsmanship on the reproduction items. Great paper. Looking forward to hearing the next one!

    1. Iohnnus (Owain) ap Gwyllim Pengryth

      Thank you, I have a couple more papers in the works, Happy to share what I have learned.

  3. Ciar ingen Fiachnae

    Wow! That is a lot of recreation and craftsmenship! I enjoyed the videos, they helped both to understand the visual and to see how they were used, especially with the dodecahedron

    I know there is reference to two of the same tool type being from the 2nd and 3rd CE, are there dates associated with the rest of the tools?

    1. Iohnnus (Owain) ap Gwyllim Pengryth

      Oh, Sorry. I realized it wasn’t in there when you mentioned it.
      Arguably the Groma’s functional origin dates to Egypt in the pre/early classical past. The Merchet instrument which is a plum bob with a squared rigid backframe to determine a true vertical line. Experimentation from there developed the Groma through Egypt and Greece. This process began prior to the development the pyramids, as there is some evidence that some form of Merchet was used in their construction. (2560 BCE – Completion of the great pyramid of Giza).
      Evidence of the water level as a separate instrument may date almost to that time as well. Certainly Archimedes (287-212 BCE), famous for quite a selection of maths and physics, Was well known for describing the effects of it’s use in the language of mathematics. At least by his time the water level in near identical form was used for engineering.
      Dioptera the word traces to Greece, As a more accurate and specialized tool, its origin dates at least to the first couple of centuries BCE.
      Roman Dodecaheadron finds all seem to fit in the 1st cen. BCE to the same CE.

  4. Your paper and videos demonstrate your deep investigations into roman surveyor’s equipment as well as other clerical tools (wax tablet) and arms! I would be interested in seeing a demonstration of setting up a roman camp using the methods and tools you have made.
    I have enjoyed visiting roman legion camps at An Tir West War, that were set up in historical fashion.
    Thank you for sharing!

  5. Wonderful presentation. I learned a lot. Of course, I mentally compared much of what you present to what I know of both modern engineering and the little bit I know from ancient China. It would be fun to compare notes.

    Curious as how you came by your dodecahedron? Curious also as to the potential for using a candle flame to determine “up”. Wouldn’t any candle holder suffice? Or are there graduations on the dodecahedron that might offer clues?

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