Gregorian chant originated as monophonic sacred music in the Catholic Church. Over centuries, church music became more complex with the addition of multiple voice parts and instruments. Secular music also grew out of folk traditions blending with religious music. Opera developed from madrigals and sacred music traditions, combining drama, poetry, and polyphonic vocal music. Monteverdi composed the first successful operas in the early 1600s, helping make opera a popular art form. Opera traditions included Italian opera seria, German Singspiel, and incorporated elements of oratorio, mass, and hymns. Mozart was a highly influential composer of the Classical period who wrote operas and other works that are still performed today.