Halloween has its roots in ancient European traditions.
It originated with Samhain (pronounced sow-in), the Celtic festival where people would put on costumes and light bonfires to ward off ghosts.
The Celts celebrated the new year on 1 November. This signaled the end of the harvest and summer, as well as the arrival of cold, dark winter. Human death frequently accompanied the bitter winter months.
Celts believed that ghosts of the departed returned to our plane of existence on October, the night before their new year.