The Roman Road Project - The Answer Is Blowing in the Wind

As much as I enjoy carrying large rocks far distances through the mud (that's a joke), building the actual road was not nearly the most interesting part of the Roman Road Project. By far, the most exciting thing was learning to use a GROMA, the ancient Roman surveying tool. Dr. Courtney Roby had explained how to use one as she does in her Roman technology class at Cornell University (I talked about how integral my conversation with her was in another post). I remember her telling me that one of the issues she had was steadying the swinging lines used to sight the rods in a straight line. I had read that the Romans used little pots of oil to steady the sway of the plum bobs attached to the ends of the lines. Despite the fact that neither Tyson, my DOTD expert, nor I thought this method would work, we decided to give it a try.

It was a sunny, clear day when we set out on our first day of surveying. Tyson had brought some old transits to show the students how things were done in the olden days. He also talked about new laser transits in use today. Looking through the scope on the transit, the students were amazed at how far they could see with such great detail.

 

We used the groma to mark the outlines of the road from one point to another. We didn't have to do the more complicated procedure of setting up right angles for the corners of towns, forts, or buildings as the Romans did. In the picture below, 6th-grade Roman technologist Warren is sighting the green lines of the groma with the rod that Tyson is holding in the distance.

So, here's what was going on near the ground to make these lines work. 8th grader Skylar is performing this same procedure from the other direction. You can see the oil pots set up below the groma.

We tried using the groma without the oil first, and we quickly discovered that it was nearly impossible to get the lines to quit swinging even with little to no wind blowing. This realization prompted our decision to try the oil.

We set up small bowls of oil on top of blocks of wood that I normally use for stone cutting. We stacked as many as needed to get just the right height for the plumbs to hang into the oil ever so slightly. Sometimes this required stacking smaller pieces of wood we were using as our rods to align the road. I imagine the Romans needing a set of wood pieces to carry around with their groma setup for this very purpose.

After all these machinations, Tyson and I laughing at the absurdity of this method, we finally got the plumbs hanging in the oil, and...something amazing happened. The lines stopped swinging immediately, the motion of the plumb bobs being stopped by the density of the oil. Tyson and I were stunned. I'm sure the Romans would have used olive oil. I had brought some cooking oil because I hate to waste good-quality olive oil. I wasn't expecting this experiment to work at all. I was so sorry I didn't have olive oil to try out and compare. Just for fun, we also tried water which did not work. The students jumped to explain the difference between oil and water - they are so smart!

To me, this day was the best on the project. We used actual experimental archaeology to figure something out.