Caesar's Rhine bridges

Caesar's Bridge across the Rhine, the first two bridges to cross the Rhine River on record, were built by Julius Caesar and his legionaries during the Gallic War in 55 BC and 53 BC. Strategically successful, they are also considered masterpieces of military engineering.

During Caesar's 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 Ubians, an allied German tribe across the Rhine. While he could have crossed the river by boats which the Ubians had offered to provide, he decided to build a bridge, thus demonstrating Rome's ability to bring the fight at any time to the Germanic tribes and additionally, as he indicated in his Commentary on the Gallic War, this approach conformed more to his own dignity and style, than to anything else.

The construction of Caesar's first bridge took place most likely between Andernach and Neuwied, downstream of Koblenz on the Rhine River. Book 4 (Liber IV) of his commentaries gives technical details of this wooden beam bridge. Double timber pilings were rammed into the bottom end of the river by winching up a large stone and releasing it, thereby driving the supporting posts (or piling) 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. 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 (roughly 460 to 1,300 ft), and its width 7 to 9 m (23 to 30 ft). The depth of the river can reach up to 9.1 m (30 ft).

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