Colossal marble head of Emperor Constantine the Great
Christian persecution was ended by Constantine in all territories of the Empire. Personal devotions of Constantine I were focused on the war god Mars, and increasingly so the god Apollo considered an unconquered sun.
Emperor Constantine I was exposed to Christianity by his mother, St, Helena.
Constantine took over the role of the patron for the Christian faith in 325
The emperors bore the image of "Sol Invictus" in their personal medallions. Constantine decreed March 7 year 321 as the "Day of the Sun" in all imperial territories. The decree ordered all judges and other people to rest. All workshops and barns were closed to their operators who could relax with their families, with the exception of agricultural and livestock activities. The other activities were illegal with the possible loss of the right to entry to heaven.
Remember the vision of Constantine the day before the "Battle of the Milvian Bridge", which took place between the Roman Emperors Constantine I and Maxentius. Constantine said he saw a cross in the sky and heard a voice telling him that if he used the cross as their flag banner, get the victory, ending the triumvirate and unify the Roman Empire.
The Milvian Bridge (Ponte Milvio) (over the Tiber, north of Rome, where Constantine and Maxentius fought in the Battle of the Milvian Bridge
Constantine won the battle and started on the path that led him to end the Tetrarchy and become the sole ruler of the Roman Empire. Maxentius drowned in the Tiber during the battle.
Constantine's victory was attributed to Christianity. Many interpretations were applied to declare that the day of Sol Invictus should be December 25th.