The god Mercury opens Plautus's Amphitryon with a prologue of the play's background events. Amphitryon and his slave Sosia are returning to their native city of Thebes following a long period fighting a war abroad. While he was away, the god Jupiter, struck by the beauty of Amphitryon's wife, Alcmena, decided he must have her. Summoning his divine powers, the god disguised himself as her absent husband and enjoyed her with impunity.
Aware that Amphitryon will soon return, Jupiter orders his son Mercury to delay his arrival so that the god might further prolong his idyll. Mirroring his father's action, Mercury takes on the appearance of Sosia. When the real Sosia encounters his own image in Mercury, the two fight, and the god beats him badly. The baffled slave makes haste to his master's ship to report this bizarre turn of events to a skeptical and angry Amphitryon.
Still in a sour mood, Amphitryon arrives with Sosia at his home the next morning, just after the departure of Jupiter. Alcmena is confused that her husband, who had seemingly just left, has returned so quickly. Although at first equally confused, Amphitryon soon realizes that his wife has been unfaithful and becomes much angrier. Alcmena's confusion only worsens, since she believes she has was never unfaithful to her husband. The couple engage in a fierce war of words until Alcmena, believing herself the wronged party, is on the verge of leaving her husband. Amphitryon heads for his ship to get support for his position from his fellow soldier Naucrates, who is also his wife's kinsman.
Aware of all, Jupiter realizes he needs to solve the problem he created. Again taking on the guise of Amphitryon, he tries to deflect Alcmena's anger, apologizing to her for his recent behavior and begging her not to leave him. At length, she agrees.
Meanwhile, failing to locate Naucrates, Amphitryon returns home, and after wrangling with Mercury, and fighting with a Jupiter still disguised as himself, he is struck by the god with lightning. He awakens to find that his wife has given birth to two children; one, fathered by Jupiter, is Hercules, and the other is the son of Amphitryon. He is deeply honored by this shared paternity and, realizing that he and his family are now under the protection of Jupiter, rejoices in the event.
Amphitryon, a Theban, joins the army of Thebes to fight against the Teloboans. When he leaves for the wars, his wife Alcmena, daughter of Electryon, is pregnant. Nevertheless, in the absence of Amphitryon, Jupiter falls in love with Alcmena and decides that he must enjoy her favors. Disguising himself as Amphitryon, Jupiter appears to Alcmena as her husband, just returned from a battle with the Teloboans. Alcmena is unable to recognize the impostor and welcomes Jupiter as her husband. Because Jupiter wishes to enjoy Alcmena as long as possible, he has the sun, moon, and stars remain fixed, and so the night he spends with Alcmena is long enough for her to conceive and be ready to bring forth a child by Jupiter at the same time she gives birth to the child by her husband.
In the meantime Amphitryon’s ship returns to Thebes. It is still night, so Amphitryon’s slave, Sosia, fearfully walking the streets of the sleeping town, tries to console himself with the pleasantness of the news he is bringing to its citizens. He thinks how well his master, Amphitryon, handled the war with the Teloboans, how the enemy refused to arbitrate the dispute over lands, how the battle was joined, and how Amphitryon was awarded the golden cup of Pterela as a token of the valor displayed in the battle.
While Sosia soliloquizes, Mercury, disguised as Sosia, is listening to every word. Mercury assumes the disguise to aid his father, Jupiter, in the latter’s scheme to make love to Alcmena. As Sosia comes through the streets to Amphitryon’s house, Mercury, in the guise of Sosia, is guarding the house and the inmates against any disturbance. When Sosia sees Mercury he is afraid, but he goes up to...
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