"Coin of Emperor Constantine I depicting Solis Invictus with the legend SOLIS INVICTO COMITI, c. 315
"Emperors portrayed Sol Invictus on their official coinage, with a wide range of legends, only a few of which incorporated the epithet invictus, such as the legend SOLI INVICTO COMITI, claiming the Unconquered Sun as a companion to the Emperor, used with particular frequency by Constantine.[31] Statuettes of Sol Invictus, carried by the standard-bearers, appear in three places in reliefs on the Arch of Constantine.
"Constantine's official coinage continues to bear images of Sol until 325/6. A solidus of Constantine as well as a gold medallion from his reign depict the Emperor's bust in profile twinned (jugate) with Sol Invictus, with the legend INVICTUS CONSTANTINUS[32]
"Constantine decreed (March 7, 321) dies Solis—day of the Sun, "Sunday"—as the Roman day of rest (Codex Justinianus 3.12.2):
"On the venerable day of the Sun let the magistrates and people residing in cities rest, and let all workshops be closed. In the country however persons engaged in agriculture may freely and lawfully continue their pursuits because it often happens that another day is not suitable for grain-sowing or vine planting; lest by neglecting the proper moment for such operations the bounty of heaven should be lost.[33]
"Constantine's triumphal arch was carefully positioned to align with the colossal statue of Sol by the Colosseum, so that Sol formed the dominant backdrop when seen from the direction of the main approach towards the arch.[34]"
Sauce: https://en.wikipedia.org/wiki/Sol_Invictus#Christianity