[1][2] From Aurelian onward, Sol Invictus often appeared on imperial coinage, usually shown wearing a sun crown and driving a horse-drawn chariot through the sky.

[a] The last known inscription referring to Sol Invictus dates to AD 387,[4] although there were enough devotees in the fifth century that the Christian theologian Augustine found it necessary to preach against them.

Sol Invictus, on the other hand, was believed to be a Syrian sun god whose cult was first promoted in Rome under Elagabalus, without success.

[10][11][12][13] Invictus ("unconquered, invincible") was an epithet utilized for several Roman deities, including Jupiter, Mars, Hercules, Apollo, and Silvanus.

[13]: 18  The Roman cult to Sol is continuous from the "earliest history" of the city until the institution of Christianity as the exclusive state religion.

[15] An inscription of AD 102 records a restoration of a portico of Sol in what is now the Trastevere area of Rome by a certain Gaius Iulius Anicetus.

[b] Another, stylistically dated to the 2nd century, is inscribed on a Roman phalera (ornamental disk): INVENTORI LUCIS SOLI INVICTO AUGUSTO ("I glorify the unconquerable sun, the creator of light.

[23]: 203 According to the Historia Augusta, Elagabalus, the teenaged Severan heir, adopted the name of his deity and brought his cult image from Emesa to Rome.

[29] After his victories in the East, the Emperor Aurelian thoroughly reformed the Roman cult of Sol, elevating the sun-god to one of the premier divinities of the Empire.

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.

His successors automatically inherited (or sometimes acquired) the same offices and honours due to Octavian as "saviour of the Republic" through his victory at Actium, piously attributed to Apollo-Helios.

[j] According to some scholars, the emperor Aurelian instituted in AD 274 the festival Dies Natalis Solis Invicti ('birthday of the Invincible Sun') on 25 December,[44] the date of the winter solstice in the Roman calendar.

[45] Gary Forsythe, Professor of Ancient History, says "This celebration would have formed a welcome addition to the seven-day period of the Saturnalia (December 17–23), Rome's most joyous holiday season since Republican times, characterized by parties, banquets, and exchanges of gifts".

[45] Before Aurelian, the Calendar of Antiochus of Athens, c. second century AD, had marked 25 December as the "birthday of the Sun" but did not refer to any religious festival being held on that date.

Historians generally agree that this part of the text was written in Rome in AD 336,[44] and most scholars see this as referring to the Natalis Solis Invicti.

[50][k][53] Aurelian also instituted the Agon Solis (sacred contest for Sol), held every fourth year, as St Jerome's Chronicon attests.

[54] In AD 362, the emperor Julian wrote in his Hymn to King Helios that the Agon Solis was held in late December, between the end of the Saturnalia and the New Year.

Steven Hijmans argues that the earliest certain evidence for a festival of Sol Invictus on December 25 is from Julian, thirty years later; he suggests that the pagan feast might have been a reaction to the Christian one rather than vice versa.

He is shown in floor mosaics, with the usual radiate halo, and sometimes in a quadriga, in the central roundel of a circular representation of the zodiac or the seasons.