Os Encantos de Medeia (Medea’s Spells) was performed in the Bairro Alto theatre in May 1735. António José da Silva drew inspiration from Salomon and Pellegrin’s libretto Médée et Jason (Medea and Jason). The opera had met with great success on its premiere in 1713 and featured a few spectacular scenes whose influence is evident in da Silva’s play, particularly when the demons transform into nymphs during the third act and when a storm breaks out on the stage. Da Silva’s play is even more closely related to Francisco de Rojas Zorrilla’s comedy Los Encantos de Medea (1645), staged in 1717 in Valencia by Manuel de Fresneda (Pesoa): in this play, the sorceress also flew away on a fire-breathing dragon. As every other play by da Silva, Os Encantos was performed on music by Antόnio Teixeira. The plot develops according to a structure which da Silva systematised from 1735 onwards: a hero is torn between two beautiful women; after a moment of great danger, the “joco-séria” (playful and serious) plot ends with a marriage. The valet Sacatrapo lives the same adventures as his master, but in a farcical mode. Thus, he makes the ram of the Golden Fleece speak in Latin, in a scene comically replicating another.

In accordance with the tradition of the baroque opera, the play shows spectacular machinery traditionally used in stagings of Medea’s story. On several instances, the characters go down from or up into the sky on a cloud; the scenes of landing and embarkation on the Argo ship are also followed by scenes at sea, and several dragons are shown. To fight one of them, Jason arrives on Pegasus’s back, in a scene of flight. Most importantly, Medeia’s (Medea) magical powers are used during an avista: to attract Jason, she makes the trees and the mountains move, splits the armies up with a river, erects a tower and summons the winds.

Traps in the stage also open and close to swallow up a dragon or the servant Sacatrapo, who loses his head in it and comes back with the head of a donkey. Da Silva explores various possibilities made possible by the use of puppets. Medea’s marvellous story creates a very spectacular performance, but taunts are also used to add a farcical dimension to it: the marvellous of the opera is therefore paralleled, discussed and even mitigated by the burlesque aspects of the play.

Jason lands in Colchis with Teseu (Theseus) and an armed escort; he seeks to obtain the Golden Fleece. As he admires the King’s beautiful daughter, Medeia (Medea), and her cousin Creúsa, his servant Sacatrapo is coveting Arpia, Medeia’s servant. Sacatrapo, hidden inside a sideboard, overhears Medeia declaring her love for Jason to her servant. Jason promises to marry Medeia if she helps him find the Golden Fleece. But he is in love with Creúsa: he declares his love to his servant and entrusts him with inquiring into the young woman’s feelings. The King is sceptical about the motifs of Jason’s coming and asks Medeia to find out about his true intentions. Because Jason urges her to, Medeia carries him on a cloud to the enchanted garden. On Pegasus’s back, Jason enters the garden, where he fights against a fire-breathing dragon; laid down, the dragon disappears into flames. Medeia summons Sacatrapo thanks to a dragon who spits the servant out of its month. Casting her spells, she makes the flowers of the garden move and transforms them into nymphs (which Sacatrapo sees as donkeys). Jason confirms again that he loves Medeia, even though he is thinking about Creúsa.

Jason is preparing to flee with Teseu and asks Sacatrapo to go fetch Creúsa. The servant tells the King that Jason stole the Golden Fleece from him. Medeia, abandoned, confides in Creúsa. The young women order Jason to explain himself. The King asks Medeia to vouch for Jason; she agrees. Sacatrapo meets Medeia: mistaking her for Creúsa during a night scene, he reveals that Jason is unfaithful. Furious, Medeia buries him slowly to feed the dragons with him, and replaces his head with a donkey’s. He must look for his head in the depths. Arpia fools Sacatrapo by promising that he will discover a donkey with golden droppings; this donkey is said to be kept by an ant. Sacatrapo is determined to kill the ant and steal the donkey using the hat given by Arpia, which should make him invisible. Medeia walks in on Creúsa and Jason during a romantic duo scene; she buries her rival inside a mountain. The King begins a war against the Argonauts: Sacatrapo arrives with a rag on his head and believes that he is invisible. He and Jason are taken prisoners. Riding a chariot drawn by dragons, Medeia divides the armies with a river. The King disowns his daughter, as she raises a tower from which she defies him. While Sacatrapo believes that he has found a treasure, snakes come out of the chest he is dragging: he has once again been fooled by Arpia. Creúsa and Jason flee during a night scene, but Medeia unleashes the winds, leading to a storm scene, so that they are forced to go back to Colchis. The King pardons Jason, offers him to marry Creúsa and promises to kill Medeia, who escapes on a cloud.