The story is ostensibly about the struggle for power in
Ancient Rome, but actually about the universal struggle between love and duty. Delphia, a
prophetess, foretells that Diocles, a footsoldier, will become emperor after he kills a "mighty
boar" and marry Delphia's niece Drusilla, who is in love with him. Diocles takes the prophecy seriously, and starts slaughtering pigs. As it turns out, a soldier called Volutius Aper (Aper=boar) has murdered the old emperor, and Diocles kills Aper in revenge. As a reward for this action he is made co-emperor and renames himself Dioclesian. He ignores his promise to marry Drusilla, and courts his co-emperor's sister the princess Aurelia instead. This angers Delphia, who brings the wedding ceremony to a stop by conjuring a storm and a monster. She then causes the princess to fall in love with Diocles' rival Maximinian, and the
Persians to defeat the Roman army. Diocles realises the error of his ways, routs the invaders, cedes his half of the throne to Maximinian, and moves to
Lombardy with Drusilla. == Instrumentation ==