I’ve always been told that the date for Christmas isn’t based on any historical date for Jesus’s birth but on pre-existing pagan solstice celebrations. So, why is Christmas on the 25th then? Why not on the 21st? No one has ever been able to explain that to me.
I was interested and found this prior response by u/gadarn.
You might also find this old post of mine interesting, in which I discuss the history of sun worship in ancient Rome: https://www.reddit.com/r/AskHistorians/comments/6xbtao/was_the_birth_date_of_sol_invictus_influenced_by/dmf21c4?utm_medium=android_app&utm_source=share