Plainchant, also called plainsong, were monophonic chants that dominated music in Christian churches in Europe until the introduction of polyphony in the ninth century. They were written with a unique form of notation that used four-line staffs and had Latin lyrics. Their non-metric rhythms were generally more free-flowing than the metered rhythms of later Western music, and they were sung without instrumental accompaniment. The best-known variety of plainchant today is Gregorian chants, which was named after, but not invented by, Pope Gregory I.