Halloween Has Roots in an Ancient Celtic Festival

The earliest precursor to Halloween is a Celtic festival called Samhain, which was celebrated midway between the fall equinox and winter solstice, and marked the day when the barrier between the real and supernatural worlds was thought to be thinnest. This connection with the otherworld meant that both the dead and dangerous spirits could cross over, or so it was believed, and so Celts wore costumes to blend in and evade harm.