Castus was a Gallic slave, who together with the Thracian Spartacus, and the fellow Gauls Crixus, Oenomaus and Gannicus, was one of the leaders of rebellious slaves during the Third Servile War (73-71 BC). He was killed along with his co-commander Gannicus and their Gallic and Germanic followers by Roman forces under Marcus Licinius Crassus at the Battle of Cantenna in Lucania in 71 BC.