Elena is a 1659 "dramma per musica" in a prologue and three acts by Francesco Cavalli. It is set to a libretto initiated by Giovanni Faustini (who died in 1651) and completed by Nicolò Minato, and it was first performed in Venice at the Teatro San Cassiano (the dedication is 26 December 1659). "Elena" was revived in 1661 in Palermo but then not heard again until 2013, at the Aix-en-Provence Festival.
Just like many other operas by Cavalli, "Elena" includes a ballo, or an Italian dance which incorporates singers, choristers, and instrumentalists. However, it soon began to be replaced by something analogous to the intermedio, sometimes incorporating a chorus. 
Plot.
The Greek prince Menelaus (nephew of the king of Crete Atreus) and Theseus, king of Athens, are in love with Helen, a woman of rare beauty, famous for the fire of Troy. Menelaus, to get closer to Helen, dresses as a woman to come and serve her by pretending to be an Amazon. One day Peritous, seeing him in women's clothes fighting with Elena and therefore believing him to be a woman, falls in love with her. Theseus kidnaps Helen, since he had sworn not to marry except with a daughter of Jupiter - and Helen was reputed to have been fathered by Jupiter in the guise of a swan. To kidnap Helen, he abandons Hippolyta, a prisoner received as a gift from Hercules and in love with Theseus, who when she goes to look for him discovers that he has kidnapped Helen and is therefore disdained and torn in her love for her. Helen will be freed by her brothers, Castor and Pollux; Hippolyta's affection strikes Theseus, who decides to marry her; Menelaus, having discovered himself, marries Helen. 
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