Sol was the sun god; identified with the Greek Helios. Originally he was a Sabine deity. The bringing of his cult to Rome (simultaneously with the cult of Luna) was attributed to Titus Tatius. The deity worship was performed by the Sabine family of Aurelius.
In the art of ancient Rome, he was most often depicted on the model of the Greek Helios, i.e. with a radiant halo around his head or a radiant crown on his head, on a golden chariot drawn by four horses.
He was nicknamed Indiges, and his festival was celebrated on August 8. A temple on the Quirinale and an altar in Circus Maximus were erected in his honour.
The cult of deity combined with the influence of Eastern religions led to the creation in the 3rd century CE. a new syncretic cult of the “Invincible Sun” (Sol Invictus). The cult of Sol Invictus was a new syncretic cult combining elements of Mithraism, the cult of El Gabal, Baal, Astarte, and the Roman solar deity Sol. He worshipped the sun as the personification of all other deities. The Sol Invictus cult was performed at the end of the empire, introduced by Emperor Aurelian.
By a decree of March 7, 321 CE Emperor Constantine the Great introduced Sunday as the official holiday Sol Invictus – dies Solis.
Sol Invictus, falling on December 25, is first authenticated in 354 CE Church at the end of the 4th century CE rewrote the celebration of Christmas on this day. It is widely claimed that the December 25th date for Christmas was chosen to deliberately remove and replace the Roman festival of Dies Natalis Solis Invicti (“Birth of the Undefeated Sun”). However, this claim is heavily criticized.