Cajo Mario is an opera seria in 3 acts by composer Niccolò Jommelli. The opera's Italian language libretto by Gaetano Roccaforte is based on Lucius Anneus Florus's Tito Livio e Plutarco. All of the parts are written for castrati, except for the title role, written for a Tenor. The work premiered on 6 February 1746 at the Teatro Argentina in Rome.
| Role | Premiere Cast Conductor: |
|---|---|
| Cajo Mario | Litterio Ferrari |
| Marzia | Giuseppe Chiaramonte |
| Annio | Gioacchino Conti |
| Rodope | Giuseppe Casoni |
| Lucio | Domenico Giardini |
| Aquilio | Alessandro Veroni |