Complex sentence: The song is based on "The Iliad" by Homer and on the "Aeneid" by Virgil, and narrates the final days of Troy, as foreseen by Cassandra, daughter of the king of the destroyed city.
Split into simpler sentences: The song is based on "The Iliad" by Homer and on the "Aeneid" by Virgil. The events described in the song are the visions of the final days of Troy, as foreseen by Cassandra, daughter of the king of the destroyed city.