The tyrant Tarquinio has recently been deposed from the throne of Rome for his many abuses of power and has allied with King Porsena of the neighbouring kingdom of Etruria. Together they have marched on Rome with their armies and are attacking the city to restore Tarquinio as King of Rome. The good natured and trusting King Porsena has been duped by Tarquinio and does not see with what a scoundrel he has allied himself- indeed, Porsena has even promised his daughter, Princess Irene, in marriage to Tarquinio.