Science Week 2014: Amazing Arches!

Roman arches don’t seem like they should be particularly scientific. Stacking blocks into an arch isn’t something that most people think of as “Roman science”. In truth, building Roman arches required some serious physics!

               

The first thing to know about Roman arch science is that the Romans built two different of arches; voussoir and corbel. Voussoir arches are made up of lots of individual blocks of stone, the voussoirs, specifically shaped to be widest at the top. These are arranged into a semicircle, with some sort of solid support at either end, to make the well-known “Roman arch” shape seen in many places around the Baths. 

A voussior arch.

 A corbel arch is much simpler; it’s just two pieces of stone, one resting on the other, positioned into a triangular arch. 

A corbel arch.

But how did arches work, and why were they important to the Romans? The reasons are to do with how the blocks interact with each other, and how that made them important architectural supports. In a voussoir arch, each voussoir shares force with its neighbours. If force is put on the arch, each voussoir leans into the next voussoir down the arch. Therefore, each voussoir is supporting its neighbour on one side, and being supported by its neighbour on the other. This means that as long as the voussoirs are mortared to prevent them falling out of the arch and there is support independent of the arch at each end, the arch will hold much more weight than its size would suggest.   

The physics of a voussoir arch.

In a corbel arch, the force is also divided, but a corbel arch holds because it is not divided equally. The supporting piece takes most of the force, preventing the part that makes the actual arch from being overburdened. Therefore, as long as the supporting part is strong enough, the arch holds. 

The physics of a corbel arch.

However, the more force you want on a corbel arch, the larger a supporting part you need, and the taller the arch is. This makes it more space-efficient to use voussoir arches, and as a result they are more common in Roman architecture.

All of this shows that Roman arches were very scientific constructions, despite appearing very simple!