1.1.1Caesar and his Rhine Bridge
From 58 to 50 bc, during his conquest of Gaul, Julius Caesar (100–44 bc) led his Roman legion into a series of wars to quell the threat posed by the hostile Gallic tribes and other neighbouring forces.
In 55 bc, as a reaction to the constant harassment by some German tribes at the boundary of Roman Gaul, Caesar decided to lead his legion across the Rhine.
A natural boundary between Gaul and the German tribes, the Rhine was known for its great depth, width, and the rapidity of its flow. Although crossing by boat would have been less of a problem, to Caesar this was unsafe and undignified. He determined to make the effort to build a bridge – only then could he frighten the reckless and combative barbarians.
The exact location of the bridge is not clear today; most suggestions point to the area between Andernach and Koblenz, in a comparatively open part of the Rhine Valley. Accordingly, the length of the bridge is speculated to have been between 200 and 400 metres.
The bridge was built in ten days including the collection of timbers. Caesar led his legion over the river, took his revenge on the Germanic villages and struck fear into the Germans. He then led the army back to Gaul and destroyed the bridge. The action was a great military success.
In his Commentarii de bello gallico (Gallic Wars), the report written by his own hand in third-person narration, Caesar described the construction of the bridge with an engineer’s precision and in great detail:
In the text, Caesar described a form of trestle bridge with inclined posts in pairs on either side, holding a beam in between. Though written in a detailed and accurate manner, in places, the description is confusing to later readers. The most disturbing term is “fibulis” (plural of “fibulae” or “fibula”), which describes the elements used in pairs at the joints of the middle beam and the posts. Thanks to this particular device, the structure would be even more stable against the thrust of the river water.
There is no satisfactory contemporary definition of the word “fibulis.” A similar term, “fibula,” and its plural form “fibulae,” meaning brooch or pin for fastening garments, might be one of the closest definitions. In the legion, they may have symbolized specific ranks or positions in the Roman army.
Two millennia later, when modern scholars shone the spotlight on Caesar’s Rhine Bridge again, they raised a series of questions including the location of the bridge, the geological environment of the site, the bridge form, the construction process, etc. Among these questions, the structure of the bridge was the topic most focused on; thus the explanation on the form and function of the fibulis served as the key.1
Although in the narration, Caesar is the bridge planner (“nationem pontis hanc instituit”/ “He proceeded to construct a bridge on the following plan”) this bridge is commonly attributed to Mamurra, his praefectus fabrum (officer in charge of engineering) at that time, a man who held this position from 58 to 54 bc (McDermott 1983, 292–307).
Our knowledge about Mamurra today mainly comes from the description by the poet Catullus: his great fortune from the spoils of wars, his extravagant and lascivious life and – probably just a rumour – his homosexual relationship with Caesar. Despite these bad reputations, Mamurra was considered “by all means the best military engineer of his day” (Frank 1928, 157–9). Among his genius inventions was also a new kind of ship which enabled Caesar’s second invasion of Britain.
There was some speculation as to whether Mamurra and Vitruvius were the same person (Thielscher 1961), although this opinion did not gain general acceptance (Ruffel and Soubiran 1962). The two do have some things in common. Vitruvius, the most well-known architect of antiquity, is the author of the first preserved architectural treatise – De Architectura (Ten Books on Architecture) –which is dedicated to his patron, the emperor Caesar Augustus. He also served in the Roman army as praefectus fabrum under Julius Caesar and was good at designing military constructions and machines. But among other factors that led to the refutation of identifying these two names as one man was the fact that Vitruvius apparently held a much less prominent position than Mamurra. Besides, the Rhine Bridge gives Vitruvius another “alibi.” In his De Architectura, in the tenth book he wrote on military architecture and engines, mainly derived from his experience with C...
