Some early Christian writers connected the sun to the birth of Jesus, which Christians believe was prophesied in Malachi 4:2 as the "Sun of Righteousness." "O, how wonderfully acted Providence that on that day on which that Sun was born...Christ should be born", Cyprian wrote. In the fourth century, John Chrysostom commented on the connection: "But Our Lord, too, is born in the month of December ... the eight before the calends of January [25 December] ..., But they call it the 'Birthday of the Unconquered'. Who indeed is so unconquered as Our Lord ...? Or, if they say that it is the birthday of the Sun, He is the Sun of Justice."
One ancient source mentioned Dies Natalis Solis Invicti in the Chronography of 354, and Sol scholar Steven Hijmans stated that there is no evidence that the celebration precedes that of Christmas: "[W]hile the winter solstice on or around December 25 was well established in the Roman imperial calendar, there is no evidence that a religious celebration of Sol on that day antedated
Dies Natalis Solis Invicti means "the birthday of the unconquered sun". Sol Invictus
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For for history of open http://en.wikipedia.org/wiki/Christmas#Pre-Christian_background