Calto is a comune (municipality) in the Province of Rovigo in the Italian region Veneto, located about southwest of Venice and about west of Rovigo. As of 31 December 2004, it had a population of 834 and an area of .
Calto borders the following municipalities: Castelmassa, Ceneselli, Felonica, Salara, Sermide.
Calto is an opera seria in 3 acts by Francesco Bianchi. The libretto was by Giuseppe Maria Foppa, after the 'celtic' poetry of Ossian. The opera was first performed at the Teatro San Benedetto in Venice on 23 January 1788.
Calto was an innovative work with some special instrumentation. As Marita P. McClymonds explains "Bianchi uses flat keys, fluctuating modes, chromatic dissonances and an unusually wide range of wind timbres (oboe, bassoon, clarinet, horn and English horn) for maximum dramatic effect."