Halloween's origins date back more than 2,000 years. On what we consider November 1, Europe's Celtic peoples celebrated their New Year's Day, called Samhain (SAH-win).

On Samhain eve—what we know as Halloween—spirits were thought to walk the Earth as they traveled to the afterlife. Fairies, demons, and other creatures were also said to be abroad.

In addition to sacrificing animals to the gods and gathering around bonfires, Celts often wore costumes—probably animal skins—to confuse spirits, perhaps to avoid being possessed, according to the American Folklife Center at the U.S. Library of Congress.

By wearing masks or blackening their faces, Celts are also thought to have impersonated dead ancestors.

Young men may have dressed as women and vice versa, marking a temporary breakdown of normal