As governor of Gallia Narbonensis, he plundered the temple of the Celtic Apollo at Tolosa (Toulouse), which had joined the Cimbri.
In 105, Caepio suffered a crushing defeat from the Cimbri at Arausio (Orange) on the Rhone, which was looked upon as a punishment for his sacrilege; hence the proverb Aurum Tolosanum habet, of an act involving disastrous consequences.
From 104 to for he served again under Marius in the war with the Cimbri and Teutones and fought in the last great battle in the Raudian plains near Verona.
Ridgeway (Early Age of Greece, 1901) considers that the Belgic tribes were Cimbri, "who had moved directly across the Rhine into north-eastern Gaul."
In 101 the Cimbri were defeated on the Raudine plain, near Vercellae, by the united armies of Catulus and Marius.