In the fourth century, after Christianity was legalized in 313 by Emperor Constantine I, who became a Christian himself and began building churches and monuments to the martyrs, public devotion to the martyrs began to flourish. Their graves became churches and places of pilgrimage and prayer. On May 13, 609, Pope Boniface IV transformed the Pantheon in Rome, a former pagan temple, into a church dedicated to the Blessed Virgin Mary and all martyrs. The annual celebration of its dedication also honored the Blessed Virgin Mary and all martyrs. On November 1, 731, Pope Gregory III dedicated an oratory within Saint Peter’s Basilica to “all saints” that included the Apostles, martyrs, confessors, and all holy men and women throughout the world. This broadened the commemoration of the saints beyond the martyrs to all who lived saintly lives. In 844, Pope Gregory IV extended the November 1 celebration to the entire Church. In 1484, Pope Sixtus IV made November 1 a holy day of obligation for the entire Church.