Caesar's Rhine bridges

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Likely site of Rhine crossings

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Caesar’s Rhine bridges, the first two bridges to cross the Rhine River, were built by Julius Caesar and his legionaries during the Gallic War in 55 BC and 53 BC, respectively. Strategically successful, they are also considered masterpieces of military engineering.^[1]

During the conquest of Gaul it became necessary to secure the eastern border of the new provinces against marauding Germanic tribes. The tribes felt safe on the eastern side of the Rhine river, trusting the river as a natural border which offered cover from retaliatory attack after their opportunistic raids into the province. Caesar decided to confront them. He also wanted to show support for the Ubii, an allied German tribe across the Rhine. While he could have crossed the Rhine by boat, he decided to build a bridge. By this he demonstrated the might and power of Rome. In addition, as he indicated in his Commentary on the Gallic War, this approach conformed more to the dignity of the Roman Army.

The actual construction of Caesar's first bridge took place most likely between Andernach and Neuwied, downstream of Koblenz. Liber IV of his commentaries gives technical details of this wooden beam bridge. Double timber pilings were rammed into the bottom of the river by winching up a large stone and releasing it, thereby driving the beam into the riverbed. The most upstream and downstream pilings were slanted and secured by a beam, and multiple segments of these then linked up to form the basis of the bridge. Conflicting models have been presented based on his description.^[1]^[2] Separate upstream pilings were used as protective barriers against flotsam and possible attacks while guard towers protected the entries. The length of the bridge has been estimated to be 140 to 400 m, and its width 7 to 9 m. The depth of the river can reach up to 9.1 m.

The construction of this bridge it showed that Julius Caesar could go anywhere and that Rome could go anywhere. Since he had over 40,000 soldiers at his disposal, they built the first bridge in only 10 days using local lumber. He crossed with his troops over to the eastern site and burned some villages but found that the tribes of the Sugambri and Suebi had moved eastward. After 18 days and without any major battle he returned to Gaul and cut the bridge down.

Two years later, close to the site of the first bridge, possibly at today's Umitz (near Neuwied), Caesar erected a second bridge, built "in a few days", as described in Liber VI. His expeditionary forces raided the country side but did not encounter significant opposition as the Suebi retreated. Upon returning to Gaul, the bridge was taken down again.

Caesar's strategy was effective, as he was able to secure the eastern border of Gaul. He demonstrated that Roman power could easily and at will cross the Rhine and henceforth for several centuries significant Germanic incursions across the Rhine were halted. Further, his feat served him in establishing his fame at home.

With Roman colonization of the Rhine valley more permanent bridges were built later at Cologne, Koblenz, and Mainz.

Later speculation about their location is due to the temporary nature of the construction and the lack of a precise location in Caesar's report. However diggings in the Andernach-Neuwied area found residual pilings that are considered to be remnants of Caesar's bridges. As an alternative site a place south of Bonn has been mentioned.^[1]