Clastidium (modern Casteggio), was a village of the Ligurian tribe of Anamares (Marici named also) in Gallia Cispadana, on the Via Postumia, 5 miles east of Iria (modern Voghera) and 31 miles west of Placentia.
Here in 222 BC, Marcus Claudius Marcellus defeated the Gauls and won the spolia opima; in 218 BC, Hannibal took it and its stores of grain by treachery. It never had an independent government, and not later than 190 BC was made part of the colony of Placentia, founded in 218 BC.
The Battle of Clastidium was fought in 222 BC between a Roman army led by the consul Marcus Claudius Marcellus and a Celtic force of the transalpine Gaesatae, called by the cisalpine Insubres. The Gaesatae were led by Viridomarus (Florus) or Britomartus (Plutarch), as the name varies in translation. The Romans won the battle, and in the process, Marcellus earned the spolia opima, one of the highest honors in ancient Rome, by killing the king in single combat. It was also notable as one of the few battles won by the Roman cavalry without any aid by the legions.
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