The main sources for the story told in Busenello's libretto are the "Annals" of Tacitus; book 6 of Suetonius's history "The Twelve Caesars"; books 61–62 of Dio Cassius's "Roman History"; and an anonymous play "Octavia" (once attributed to the real life Seneca), from which the opera's fictional nurse characters were derived. The main story is based on real people and events. According to the analyst Magnus Schneider, the character of Drusilla was taken from Girolamo Bargagli's 16th-century comedy "The Pilgrim Woman".