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Bridge over the River Arar

In Sunday’s posting, the main character is involved in an engineering project to construct a bridge over the Arar River (today, called the Saône).

Most who have any exposure to ancient Roman culture or history are likely well aware of the marvels of Roman engineering, from concrete structures that are still standing—at least in part—to hundreds of miles of aqueducts and thousands of miles of roads. Most are probably also aware that the Roman military was heavily involved in various construction projects, including both Hadrian’s and Antonine’s Walls in Britain, as well as others.

Many of these structures are tremendously impressive, but probably less well-known are some of the temporary engineering projects that Roman legions constructed, structures that were designed for a single purpose and then either left alone (and likely were demolished over the centuries after), or deliberately dismantled to prevent their use by the enemies of Rome. The “Bridge over the River Arar” is one such structure.

For a little background, the Romans had denied migrating Helvetii tribes permission to cross Roman lands to move westward, and had turned north through mountain passes north of Geneva to bypass “Farther Gaul” (as the Romans called their lands in Gaul north of the Alps). As they did so, they are accused of having ravaged lands of Roman allies in the area, and so Caesar went back to Illyricum to retrieve three of his legions, as well as “Nearer Gaul” (Cisalpine Gaul, the region of Gaul south of the Alps, today northern Italy) and retrieved the two newly mustered legions (XI and XII), and marched to meet the one legion still in “Farther Gaul” to intercept the Helvetii.

They arrived a bit south of where the Helvetii had been crossing the Arar River for twenty days, and found that about a quarter of the Helvetii were still on the near (south, I believe) bank of the river. This happened late in the evening, or possibly even after sunset, of that 20th day of this river crossing. When the Romans arrived, Caesar sent his frontmost legion to attack the Helvetii still on the near side, who scattered into the forest without much of a fight.

That night, the legions built their camps, and in the morning constructed a bridge over the river. The construction process took a few hours, and then all six legions went back to camp, and the next morning after that marched across the bridge to continue pursuing the Helvetii.

What I—and, undoubtedly, the Helvetii—find staggering about this is that stark contrast in the amount of time it took to be able to cross the river. The Helvetii were no strangers, as humans, to river crossing. At that time in human history (with a few individual exceptions like the Rhine and Danube), most rivers were things people would have had to figure out how to deal with, whether by fording, or wading, or lashing rafts, and even by building bridges in certain cases.

Caesar’s writings later on tell us that the Helvetii were supposedly around 370,000 people of whom 92,000 were capable of bearing arms—well over the full-strength total of the six legions Caesar had, roughly 30,000–35,000 … and, some of his legions were not full-strength, having fought for years with him already. At a minimum, the Helvetii as they migrated had about a 3:1 advantage in able-bodied men, and yet it still took three weeks for them to get across. Not to cast aspersions on them, but it does seem curious that if they were hell-bent on getting to the west coast of Gaul, they didn’t work out a solution to cross this river in the minimum amount of time possible.

So, with about a quarter of the migratory tribes scattered, and the rest on the far side of the river, the legions woke up and built a bridge in a few hours. Think about that for a moment. Not only did they decide to do a thing, they had instantaneous access to sufficient engineering savvy to safely and properly construct the thing, including every step from measuring, sourcing, and fabricating the support structure to then actually implementing it—almost certainly while at least some of them were on it. Not unlike, say, building an aircraft while flying it. Maybe not as technical or dangerous as that, but similar in concept.

This kind of immediate solution to a problem comes up time and time again in Roman military history, and to me it’s really quite impressive just how astute some of the Roman military commanders (particularly Caesar, though not only him) were in using these. The US Army calls this a force multiplier. This concept is basically that you have fighting men, and there are things you can do to make those fighting men more effective. The Spartan and Allied Greek defense at Thermopylae, for example, used the terrain to make their warriors more effective, by limiting the frontage that could fight at one time—something that made other things, like the technical advantages that Greek and Spartan warriors had, like their armor and tactics, even more effective, making each man’s fight deadlier.

In any case, it’s these kinds of construction projects that really helped the Roman military survive and thrive in circumstances they probably oughtn’t to have been able to survive, let alone thrive in, and it must have been a terribly demoralizing sight for the Helvetii to see the Romans conquer in a few hours what had taken them three weeks to do.

Published inHistory