Halloween originated from the ancient Celtic festival of Samhain, marking the end of the harvest season and the beginning of winter. As Christianity spread across Europe, the Catholic Church attempted to convert pagans by incorporating aspects of their festivals into Christian holidays. All Saints Day was established on November 1st, with All Hallows Eve preceding it on October 31st. Over time, traditions like costume wearing, trick-or-treating, and carving jack-o-lanterns developed and Halloween became a secular holiday celebrated in both America and parts of Europe.