First mentioned in the 4th c. Eastern feast of All Martyrs (13 May) and attested to by St. Ephrem of Edessa († 373), this feast came to be celebrated on other days as well in the East, e.g., Easter Friday, and the Sunday after Pentecost, the day of its observance in some places in the West. In 609 or 610, the Roman Pantheon was dedicated on 13 May under the title S. Maria ad Martyres. Many see in this the origin of All Saints Day. For reasons which are unclear, Pope Gregory IV (827-844) transferred the feast from May to 1 November, adopting perhaps the English-Gallican practice dating from the first quarter of the 8th c. Rv 7:2-4, 9-14 Ps 24:1bc-4b, 5-6 1 Jn 3:1-3 Mt 5:1-12a Let us rejoice in all the men and women, blest in the eyes of the Lord (3), who celebrate the heavenly liturgy (1). They stand in God's holy place (Ps) and sing of the love the Father has bestowed upon them (2) through the blood of the Lamb.