Halloween is known and loved today as a time to wear costumes, go door to door asking for candy, and watch monster movies. But the holiday’s origins go back centuries to the enactment of All Saints’ Day, a Christian holiday. Along the way, it has also picked up traditions from Samhain, a Celtic festival celebrating the start of winter.
All Saints’ Day

The name “Halloween” began as “All Hallows Eve.” This became “All Hallow E’en,” leading to “Hallowe’en,” or Halloween. It was the evening before All Hallows Day, which was later called All Saints’ Day. (In this case, “hallows” meant “saints.”)
All Saints’ Day, a feast for all martyrs and saints, was celebrated on November 1st for the first time during the 8th century, but customs varied regarding its observance. This date was officially established for all Catholic churches in 837 by Pope Gregory IV.
Starting in the 10th century, this feast was the eve of All Souls’ Day, which soon came to overshadow it.