Happy Halloween! 🎃 Lets reclaim the day and its Catholic origins!
In the eighth century, on the vigil of the Latin Feast of All Saints, Pope Gregory III dedicated a chapel in St. Peter Basilica to all saints. A century later, Pope Gregory IV declared this celebration a holy day of obligation in the Latin Church. He also adopted the tradition of Germanic Catholics, changing the date from May to November. Thus, the vigil of this feast shifted to the last day of October, our current Halloween day.
This article offers an excellent discussion: https://denvercatholic.org/the-catholic-origins-of-halloween/