Assertion: libretto | /r/HasProperty | set by nearly 40 composers
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text: Metastasio's libretto had already been set by nearly 40 composers; the story is based on the life of Roman Emperor Titus, from some brief hints in The Lives of the Caesars by the Roman writer Suetonius, and was elaborated by Metastasio in 1734 for the Italian composer Antonio Caldara.