Mithra is a god that i believed was born on 12/25. According to Wikipedia:
Mithra
[. . .] "Anahita, the Immaculate Virgin Mother of the Lord Mithras".
Sol Invictus
[. . .] Deus Sol Invictus [. . .] was a religious title applied to at least three distinct divinities during the later Roman Empire; El Gabal, Mithras, and Sol.
The Sol Invictus festival ran from December 22 through December 25. Eradicating the remnants of this much-celebrated pagan holiday is likely the reason why Christmas was picked by the early Catholic leaders as the birthday of Jesus Christ.
But the evidence a little more far-fetched than i remember. The date seems arbitrary in light of this.