Gregorian chant was the main form of sacred music in the Middle Ages. It consisted of a single, unaccompanied melodic line without harmony. Chant was taught orally until Guido d'Arezzo invented the four-line staff musical notation system in the 11th century, making chant the first written music. The Catholic Church was the center of musical life, and chant represented the voice of the Church. Three main styles of chant - syllabic, melismatic, and neumatic - varied based on the relationship between syllables and notes.