Complex sentence: Melani was a favorite composer of Cardinal Giulio Rospigliosi (later Pope Clement IX) and the Papal conclave of 1667 commissioned him to write an opera (title now unknown) for Carnival of 1668.
Split into simpler sentences: Melani was a favorite composer of Cardinal Giulio Rospigliosi (later Pope Clement IX). The Papal conclave of 1667 commissioned him to write an opera (title now unknown) for Carnival of 1668.