The Battle of the Arar was fought between the migrating tribes of the Helvetii and six Roman legions under the command of Gaius Julius Caesar in 58 BC. It was the first major battle of the Gallic Wars and ended in a tactical victory for the outnumbered Roman army.
Background
When Caesar became governor of the provinces given to him by the Roman Senate, three of his four legions were in northeastern Italy guarding against potential threats from Thracian tribes. The Transalpine Gaul Province, however, was guarded by a single legion and exposed to invasions by the enemies of Rome.
After the battle, the Helvetii failed to negotiate a peaceable agreement permitting their travel and resumed their migration west to Gaul. As a result, Caesar quickly bridged the river Arar and pursued the Helvetii for over two weeks until he was forced to divert his army to the city of Bibracte to replenish provisions. As Caesar's army traveled to Bibracte, the Helvetii tried to take advantage of the situation and attack Caesar's legions while they were in transit. In their effort to destroy the Roman legions, the Helvetii were unsuccessful in the battle that took place and suffered a major defeat.