[3] The action is set in the Gothic Wars and is based on the conflict between king Totila of the Ostrogoths and the Byzantine general Belisarius.
In reality Totila sacked Rome twice, in 546 and again in 550 but the libretto is not specific about whether the action is meant to take place in either of these two events or in an amalgam of them.
In the first act, set in Rome under siege, Clelia, wife of the consul Publicola, plans to resist Vitige and shows that she is willing to kill her sleeping child to prevent him falling into the hands of the invaders and then to commit suicide.
The first act ends with spectacular stage effects as a trumpet sounds, a giant elephant opens, and Belisario, Lepido and Cinna come out.
Clelia and Publicola reunite, while Belisario and Lepido declare themselves willing to renounce their love for Marzia, if Totila will become a vassal of Giustiniano.
Clelia’s conduct is unwaveringly moral; in contrast Marzia makes fun of Totila and mocks her own destiny, but eventually surrenders to both.