St. Gregory I, called the Great, was one of the most illustrious of the Popes. For fourteen years his pontificate was a model of ecclesiastical rule. He healed schisms; revived discipline; aided in the conversion of the Spanish and French Goths, and kindled anew in Britain the light of the Faith. He set in order the prayers and chant of the Church; and the Church reckons him one of her four great Doctors. He died March 12, 604. To this day the Pope when solemnizing High Mass at St. Peter’s is vested at the altar which covers the tomb of St. Gregory.

(Source: Fr. Lasance, The New Roman Missal)