Was Christmas originally a pagan holiday that was hijacked and/or have holiday hijackings happened in other instances?

by Brandbll

I've heard Jesus was actually suspected to be born in September, but it was celebrated in December to try and hijack a pagan holiday. Is this true, and regardless of whether it is or not, are there other instances of this happening in history where one religion tries to hijack another's special day?

This_Rough_Magic

Always more to say but (for fairly obvious reasons) this one comes up about once a year.

Last year there was a good answer from u/KiwiHellenist. There's also an interesting meta-answer here from the same poster about why and how people started saying Christmas was Pagan in the first place.