Gregorian chant is a type of religious singing that originated from Pope Gregory I in the Middle Ages. It involves monks singing the same notes without harmony. The monastery of Santo Domingo de Silos is famous for its Gregorian chant performances. The earliest musical notation involved writing signs called "neums" above words, which later evolved to using a four-line musical staff. Characteristics of Gregorian chant include being performed in Latin by male monks a cappella without instruments, with a free rhythm and all singers performing the same melody.