The Battle of Clastidium was fought in 222 BC between a Roman army led by the consul Marcus Claudius Marcellus and the Insubres, a Celtic people in northern Italy.

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.

[2] After the successful campaign of consuls Publius Furius Philus and Gaius Flaminius in 223 BC against the Insubres, the latter sent out ambassadors begging for peace to the Roman senate.

The Roman consuls, when the war season came, invaded the territory of the Insubres with their legions, and laid siege to the city of Acerrae, nowadays in the area of Pizzighettone, between Cremona and Lodi (south of Milan).

Thus the Romans succeeded in conquering the largest independent Celtic tribe in Italy,[3] and firmly established their hegemony over the Po Valley, then the most productive agricultural region in the peninsula.