Only in the late Roman Empire, scholars argued, did the solar cult re-appear with the arrival in Rome of the Syrian Sol Invictus (Latin: the unconquered sun), perhaps under the influence of the Mithraic mysteries.

[7][8] In Virgil he is the grandfather of Latinus, the son of Sol's daughter Circe who lived not far from Rome at Monte Circeo.

[15] Sol Invictus (English translated as "Unconquered Sun") was long thought to have been a foreign state-supported sun god introduced from either Emesa or Palmyra in Syria by the emperor Aurelian in 274 and overshadowing other Eastern cults in importance,[16] until the abolition of classical Roman religion under Theodosius I.

According to a single, late source, the Romans held a festival on December 21 of Dies Natalis Invicti, "the birthday of the unconquered one."

Since the 12th century,[26] there have been speculations that the near-solstice date of 25 December for Christmas was selected because it was the date of the festival of DIES NATALIS SOLIS INVICTI, but historians of late antiquity make no mention of this, and others speculate Aurelian chose December 25 to shadow early Christian celebrations already on the rise.

[17] Throughout the 4th century the cult of Sol continued to be maintained by high-ranking pontiffs, including the renowned Vettius Agorius Praetextatus.

[28] 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.

The radiate crown shown on some emperor's portraits on coins minted in the 3rd century was associated with Sol,[35][36] and may have been influenced by earlier depictions of Alexander the Great.

[38][dubious – discuss] Sol was most notably identified with Phoebus Apollo; such equation famously occurs in Varro and Ovid.

His works have not survived, but writing five centuries later, Macrobius reports that Nigidius argued that Sol was to be identified with Janus and that he had a counterpart, Jana, who was Luna.