The early Church tried to co-opt Pagan holidays to make it easier to assimilate pagans. The Celts and Germans celebrated the Yule Solstice. The Romans had a two week drunk called Saturnalia. Hence, Christmas is in December.
Interestingly they failed by having All Saints Day on 1 Nov. Samhaine morphed intop Halloween. And it’s still with us today.
The early Irish Church apparently celebrated All Saints on April 20. It was the Romans who set the date at November 1st and the Romans didn’t celebrate Samhain.
http://en.wikipedia.org/wiki/All_Saints
Neo-pagans put out a lot of sloppy scholarship trying to take credit for feast days! :)