Had a great week in June on site with TimeTeam. We were working on (amongst other things) Roman Bridges. I got interested in Appolodorus' (for Trajan) bridge over the Danube which is shown on Trajan's column as a timber arch and described as having spans of the order of 30m. There are a number of revised sketches on the web. I came to believe that the arch might have been built like the ones Perronet built in the 18thC and produced the model shown in the photo.
Lack of time meant it never got proper abutments! More soon.