St. Mary Major Basilica
St. Mary Major was the site of Ignatius' first Mass, which he waited one year after being ordained a priest to celebrate. He had always had a strong devotion to the Nativity of Christ and hoped to offer his first Mass in Bethlehem at the Church of the Nativity. After circumstances made it impossible for Ignatius and the companions to travel from Venice, where Ignatius was ordained, to Jerusalem, they came to Rome.
Ignatius chose St. Mary Major for his first mass because it housed the relic of the Crib, from the birth of Jesus. The relic (now under the High Altar), used to be kept in the crypt of the Blessed Sacrament Chapel called the "Sistine Chapel" from the name of its donor, Pope Sixtus V. In the crypt Father Ignatius said his first Mass, "with great feeling and divine enlightenment," on Christmas Day of 1538.