THE background is difficult to grasp without the aid of the Argument in the libretto. ‘Sosarmes King of Media falling in Love with Elmira, Daughter of Haliates King of Lydia, at the Report he heard of her Beauty, demanded her in Marriage of her Father, who readily assented: But about the Time that Elmira was preparing for her Departure to her Husband, a cruel Rebellion broke out in Lydia, which obliged the Princess to defer her Journey. The Author of this Rebellion was Argones, the eldest Son and Successor of Haliates, prompted to it by a Jealousy he entertained, that his Father intended to advance his natural Son Melus, whom he tenderly lov’d, to the Throne. When Argones had openly declared himself a Rebel against his Father, the latter was obliged to take up Arms, and besiege the City of Sardis, where his Son and the Rebels had shut themselves up, and by Treachery made themselves Masters of the Palace itself. Both the Besiegers, and those they besieged were equally obstinate …’. We learn in the course of the opera that Melo's mother was Anagilda, daughter of Haliate's trusted but treacherous old counsellor Altomaro. Elmira and her mother Erenice, Haliate's Queen, are prisoners in the palace seized by Argone; Sosarme and his forces are with Haliate's besieging army.

Act I opens in the great Square of Sardis, with Soldiers drawn up in Battalia. The city has withstood every assault, but is in danger of succumbing to famine. Argone proposes a sortie to seize supplies from the enemy. He draws his Sword, the Soldiers doing the same, and after a brief military chorus all depart. In an Appartment in the palace Erenice tells Elmira of a dream in which Hecate told her to cease weeping, since the war shall be ended this day by ‘royal blood shed by a son’. Erenice fears the death of husband or son. Elmira tries to reassure her and leaves, but returns at once with an afflicted Air: Argone is preparing a sortie. Erenice's fears are reinforced, and Elmira goes off to try to dissuade her brother. Erenice follows: if Argone will not yield to her tears, he must kill her first.