Monday Class: Building Your Measuring Rope
We started the week of measuring by preparing a knotted rope. We started with a 33 foot length of rope and ties knots every 29 inches until we had 13 knots and 12 even sections. Through configuration of this rope and the power of 12, we were able to make 3-4-5 triangles (and therefore right angles) as well as perfect squares. Through a combination of shapes and configuration, it is possible to create a shape of virtually any area using this simple tool.
Wednesday Class: Building Your Groma
On Wednesday, we created our groma using the following tools.
Individual Gear:
- 1 55″ pvc piece
- a 3-piece pvc crossbar unit
- 1 4″ pvc piece
- 1 4-way divider
- 1 each 3-D printed top and bottom brackets
- 4 screws
- yarn/string and something to cut it with
- 1 bead
- 1 steel plumb bob
- 4 10′ pvc pieces
- 4 3-D printed endcaps
- yarn/string and something to cut it with
- 8 beads
- 4 3.75″ pvc shafts
- 8 pvc butt caps (4 with drilled holes)
Group gear:
- Scissors / knives / razors
- pens
- sand / funnels
- screwdrivers
Lab: Measurement
Once assembled, the groma functioned as intended, though we quickly discovered that its effectiveness depended heavily on stability: any wind or uneven ground made precise alignment difficult. Other items used in the lab were:
- Your groma
- A wheel-on-a-stick and/or measuring tape
- 3 green poles
- Many wire flags
- Piece of chalk
Activity 1 – Making a “road”
Our first task was constructing a Roman road using only straight lines and 90° turns. Starting from our initial point, we used the groma to establish a straight path, placing stakes several strides away from the last point.
Our final road measured approximately 155m with 25 flags positioned every 6.2m.
One important realization was that once we had established two reliable points, we could continue extending a straight line without constantly resetting the groma, which greatly sped up the process.
Activity 2 – Observation zones for soothsayers
Our second task was constructing a square “observation zone” centered around a fixed midpoint.
We began by marking a center point and using the groma to create four rays extending outward at right angles. From there, we measured outward in each direction 10 meters and marked the zone with flags.
Activity 3 – Making a Grid with Roads
For the third activity, we constructed a Roman-style grid with roads dividing the sections. We began by creating a square that measured 7 meters each side. Starting from a central point, we used the groma to establish four perpendicular directions. From there, we used rope and measuring tape to mark out the corners of the square. This was the most time consuming portion.
After one square was created, the rest of the configuration was easily constructed from extending straight lines out from this square. In quick succession, we created a sort of intersection between 4 identical 7x7m squares, separated by 3m of road.
Activity 4 – Determining Area of Uneven Boundary
Our final task was measuring the area of an irregular shape, which we chose to be the landscaped section out front of Boliou Hall. To simplify the process, we first measured a large rectangular section and then adjusted for the curved portions separately. We measured the main rectangular region and then estimated the curved seating area by approximating it as a triangle-like shape.
We first created a large, irregular squared area measuring 970 square meters as shown below.
We then went over this section and “cut out” several right triangles to get a better estimate of the space. Due to time constraints and environmental difficulties from wind and irregular terrain, we were only able to cut out three such triangles. These triangles had a combined area of 217 square meters.
While more time could have yielded a better result, we were still able to start getting a reasonable estimate of the area of our region. After only one “pass” of triangles, we estimated the rough area to be 735 square meters.
| Area of Squared Section (m2) | Area of Triangles (m2) | Estimated Boundary Area (m2) |
|---|---|---|
| 970 | 217 | 735 |
This lab relied more heavily on teamwork and communication than almost any other lab we have done this term. While the geometry behind the activities was relatively straightforward, actually implementing it in a large outdoor space proved surprisingly difficult.
The biggest lesson was that while the groma was powerful, it was also cumbersome. It worked best for establishing major lines and right angles, but once those were in place, the rope often became the more practical tool. By the end of the lab, we found ourselves using the groma less and other tools such as measuring tape and rope more.
More broadly, the lab showed that ancient measurement was not simply about geometry: it was about adapting tools to imperfect real-world conditions like wind, uneven terrain, and human error. The Romans may not have had modern instruments, but they clearly developed methods that were remarkably effective when used collaboratively and carefully.
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