In the early summer of 55 BC Julius Caesar had already begun his conquest of Gaul three years earlier. At that time the eastern border of the new provinces was located on the Rhine. The Germanic tribes on the eastern side of the river launched incursions to the west under the protection provided by this natural border.
But on the other side of the river there were also tribes allied with Rome, like the Ubians. They offered Caesar ships for the legions to cross the river and attack the Germanic tribes.
The Ubians, too, who from all the nations beyond the Rhine, had sent ambassadors to Caesar and formed an alliance and given hostages, earnestly begged “to bring them help, because they were gravely oppressed by the Suebi; or, if other matters prevented him, let him at least transport his army up the Rhine '; that this would be enough for their present help and their hope for the future; (…) They promised a large number of ships to transport the army.
Julius Caesar, Comments on the Gallic War IV.16
Caesar's Rhine Bridge, by John Soane (1814)
However, Caesar rejected the offer and decided to build a bridge instead. In doing so, he would demonstrate not only his support for the Ubian allies, but also Rome's ability to carry the war whenever it wished across the border. Also, as he wrote, that he considered ships unsafe, this was more consistent with his own dignity and that of the Roman people.
Caesar, for the reasons I have mentioned, had resolved to cross the Rhine; but not to cross it in ships that he did not consider sufficiently safe, nor did he consider consistent with his own dignity or that of the Roman people. Therefore, although he had the greatest difficulty in forming a bridge, due to the breadth, speed and depth of the river, he felt that he should try it himself, or that his army should not be led in any other way.
Julius Caesar, Comments on the Gallic War IV.17
The construction was carried out between present-day Andernach and Neuwied, downstream from Koblenz, an area where the depth of the river would be up to 9 meters. Watchtowers were erected on both banks to protect the entrances, and piles and barriers were placed upriver as a measure of protection against attacks and debris carried by the current.
Caesar's 40,000 soldiers built the bridge in just 10 days on double wooden piles that were driven into the riverbed, dropping a huge and heavy stone on them as a mace. The construction system ensured that the greater the flow, the harder the bridge was held together.
Illustration of Caesar’s Rhine Bridge from “History of Rome, and of the Roman people, from its origin to the invasion of the barbarians" (1883)
Two foot-and-a-half thick logs pointed at the bottom, and as long as the river was deep, were locked together with two feet of separation; these were inserted and fitted with devices into the river, and were driven with mallets, not perpendicularly like posts, but inclined and stretched out towards the river current. Then further down, at a distance of forty feet, he would set in front of the first two others locked in the same way and struck against the force and current of the river. Both, in addition, were kept firmly separated by beams two feet thick (the space occupied by the junction of the piles), placed at their ends between two brackets on each side, and consequently that these were in different directions and fixed on opposite sides to each other, so great was the force of the work,
Julius Caesar, Comments on the Gallic War IV.17
It is not known who was the engineer responsible for this new bridge construction technique, which had never been used before. Cicero suggests in a letter that his name was Mumarra, although we cannot rule out the possibility that it was Marcus Vitruvius Polio (the architect who was the author of the famous Ten Books of Architecture ), who was meeting Caesar. It is estimated that the length of this bridge could have been between 140 and 400 meters, and its width between 7 and 9 meters.
Once it was finished, Caesar crossed with his troops to the other bank, where the Ubians were waiting for him. Then he learned that the tribes of the Sicambrians and the Suevi had withdrawn to the East, in anticipation of his arrival. Not being able to present a battle and after destroying some villages, Caesar decided to turn around, cross again the bridge and knock it down behind him. It had lasted 18 days.
A scale model of Caesar’s Rhine Bridge at The Museo Della Civilta Romana in Rome. Photo: MrJennings/Flickr
Two years later history repeated itself. Near the place where the first bridge had been and about 2 kilometers to the north (possibly next to the current Urmitz), Caesar built a second, although this time he did not elaborate on the details.
Having decided on these matters, he began to build a bridge a little higher than the place where he had earlier transported his army. Once the plan is known and established, the work is carried out in a few days due to the great effort of the soldiers. Having left a strong guard on the bridge on the side of the Trier, so that no commotion would occur between them, he led the rest of the forces and the cavalry.
Julius Caesar, Comments on the Gallic War VI.9
As before, the Suebi, seeing what was coming their way, retreated to the East again, abandoning their villages and hiding in the forests. Caesar returned to Gaul and again destroyed the bridge. Only this time he only knocked down the end that touched the eastern shore, erecting defense towers to protect the rest of the bridge.
In order not to completely free the barbarians from the fear of their return, and in order to delay his warriors, having driven back his army, he broke, over a distance of 200 feet, the far end of the bridge, which connected him to the Ubian shore, and at the end of the bridge he erected four-story towers, and placed a guard of twelve cohorts for the purpose of defending the bridge, and reinforced the place with considerable fortifications.
Julius Caesar, Commentary on the Gallic War VI.29
Reconstruction of a Roman pile driver, used to build the Rhine bridge at Ehrenbreitstein Fortress in Koblenz, Germany. Photo: Holger Weinandt/Wikimedia Commons
Caesar's strategy produced the desired effect. It demonstrated the power of Rome and her ability to cross the Rhine at will at any time. Thus Julius Caesar secured the borders of Gaul, and for several centuries the Germans refrained from crossing them.
It also allowed the Roman colonization of the Rhine Valley, where permanent bridges would later be built in Castra Vetera (Xanten), Colonia Claudia Ara Agrippinensium (Colonia), Confluentes (Coblenz) and Moguntiacum (Mainz).
Archaeological excavations carried out in the late 19th century in the Andernach-Neuwied area found remains of pilings in the Rhine (their analysis in the 20th century showed that they had been cut down in the middle of the 1st century BC), which may belong to Caesar's bridges, although the place of its location has never been able to be determined exactly.
Possible location of Caesar’s Rhine Bridge. Photo: Ekem/Wikimedia Commons
As for the Ubians, in 39 BC Marco Vipsanio Agrippa finally transferred them to the west bank of the Rhine in payment their longstanding loyalty, as they had been asking for a long time, fearing reprisals from neighboring tribes. They remained loyal to Rome throughout its history, eventually mixing with the Franks who gave rise to new kingdoms in Gaul during the Middle Ages.
This article was originally published in La Brújula Verde. It has been translated from Spanish and republished with permission.
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