Rhadamistus, son of King Parsman I of Iberia (Pharasmanes), is known for his ambition, good looks, and valor.

Parsman, fearing usurpation by his son, has persuaded Rhadamistus to make war upon his uncle, King Mithridates of Armenia, Parsman’s brother, and father of Rhadamistus' wife, Zenobia.

The Iberians invade with a large army and force Mithridates into the fortress of Gorneas (Garni), which is garrisoned by the Romans under the command of Caelius Pollio, a prefect, and Casperius, a centurion.

Pollio, swayed by Rhamistus' bribery, induces the Roman soldiers to threaten capitulation of the garrison.

Under this compulsion, Mithridates agrees to surrender to his nephew.

Rhadamistus executes Mithridates and his sons despite a promise of nonviolence, and becomes King of Armenia.