CLASTIDIUM (mod. Casteggio), a village of the Anamares, in Gallia Cispadana, on the Via Postumia, 5 m. E. of Iria (mod. Voghera) and 31 m. W. of Placentia. Here in 222 B.C. M. Claudius Marcellus defeated the Gauls and won the spolia opima; in 218 Hannibal took it and its stores of corn by treachery. It never had an independent government, and not later than 190 B.C. was made part of the colony of Placentia (founded 219). In the Augustan division of Italy, however, Placentia belonged to the 8th region, Aemilia, whereas Iria certainly, and Clastidium possibly, belonged to the 9th, Liguria (see Th. Mommsen in Corp. Inscrip. Lat. vol. v. Berlin, 1877, p. 828). The remains visible at Clastidium are scanty; there is a fountain (the Fontana d’Annibale), and a Roman bridge, which seems to have been constructed of tiles, not of stone, was discovered in 1857, but destroyed.
See C. Giulietti, Casteggio, notizie storiche II. Avanzi di antichità (Voghera, 1893).