The origins of All Saints' Day are complex and evolved over centuries:
- Early Commemorations: Early Christians commemorated martyrs, often on the anniversary of their deaths. As persecutions increased, honoring groups of martyrs became common.
- May 13th Observance: In the 7th century, Pope Boniface IV consecrated the Pantheon in Rome to the Virgin Mary and all martyrs, establishing an annual commemoration on May 13th.
- Shift to November 1st: In the 8th century, Pope Gregory III dedicated a chapel in St. Peter's Basilica to all saints and fixed the anniversary for November 1st. Pope Gregory IV later extended this observance to the entire Western Church in the 9th century.
- Possible Influences: Some historians suggest the November 1st date might have been chosen partly to Christianize existing pagan festivals occurring around that time, such as the Celtic festival of Samhain.