In the first year of his governorship of Gaul 58 BC, Caesar's presence was urgently required in Transalpine Gaul (Gallia Narbonensis) because of the movement among the Teutonic tribes which was displacing the Helvetic (Swiss) Celts and forcing them into Roman territory. the year 58 BC was therefore first occupied with a campaign in which the invaders were split in two and their forces so heavily defeated that they had to retire to their own mountains.
But no sooner was this menace dealt with another loomed on the horizon. The fierce Germans tribes (Sueves and Swabians) were crossing the Rhine and threatening to overthrow the Aedui, the Gallic allies of Rome on the northern borders of the Roman province of Transalpine Gaul.
The German chief, Ariovistus, apparently envisaged the conquest of entire Gaul and its partition between himself and the Romans.
Caesar led his legions to the help of the Aedui and utterly defeated the German force, with Ariovistus barely escaping across the Rhine with what was left of his forces.
With the Germans driven back, fear was aroused in Gaul of a general Roman conquest. The Nervii, who were the leading tribe of the warlike Belgae in the north-east of Gaul prepared an attack on Rome's forces. But Caesar received warning from friends in Gaul and decided to attack first, invading Nervian territory in 57 BC.
The Nervii fought heroically and for some time the outcome of the decisive battle uncertain, but eventually Caesar's victory proved overwhelming. It was followed by a general submission of all the tribes between the river Aisne and the Rhine.
