Casticus was a nobleman of the Sequani of eastern Gaul. His father, Catamantaloedes, had previously been the ruler of the tribe, and had been recognised as a "friend" by the Roman Senate.
Ca. 60 BC, Casticus entered into a conspiracy with Orgetorix of the Helvetii and Dumnorix of the Aedui to seize control of their respective tribes and between them rule Gaul.[1] The conspiracy was discovered and put a stop to by the Helvetii.