The origin of wearing a costume on Halloween dates all the way back to the first celebrations of Samhain. The Celts wore costumes made from the hides of animals. The purpose of wearing a costume was
because people believed that spirits could walk among the living during this time, and the people wore masks and costumes to confuse the spirits who might harm them in to thinking that they were
spirits as well. This tradition continued with the Christian holiday of All Saints Day and even to this day in Halloween.