Why do we dress up on Halloween?

Every year, kids — and sometimes adults — dress up in ridiculous outfits and storm the streets, on a mission to ring strangers' doorbells and fill bags with candy. As kids, we accept trick-or-treating as normal behavior, but the October 31 tradition is really quite strange when you think about it.

The traditions and folklore of Halloween are a hybrid of Pagan, Celtic, Catholic and ancient Roman traditions.

The holiday is thought to date to the Iron Age (around 800-600 B.C.), when the Celts and Gauls ruled parts of Great Britain and Northern France. October 31 marks the last day of the Celtic calendar, and for Celtic-folklore believers, Halloween was a day of celebration before winter, which brought the death of life and nature, and the harvest.

Related: What led to the emergence of monotheism?

Similarly, Gaelic people believed it was important to honor the dead on what was, essentially, their New Year's celebration. They called the holiday Samhain, or the "summer's end" in Old Irish, according to "Halloween: From Pagan Ritual to Party Night" (Oxford University Press, 2002).

When the Romans invaded Gaul (modern day France) and Britain in 1st century B.C., many of their festival traditions became mixed with those of Samhain. In particular, the ancient Roman festival of Pomona, the Roman goddess of fruits and gardens, was held around November 1, and celebrated the apple harvest. Scholars say traditions from the darker Roman festivals of the dead called Parentalia and Feralia, although held in February, were also incorporated as Halloween celebrations spread through Europe.

In the Roman Catholic Church, All Saints' Day, which is also referred to as All Hallows or Hallowmas, is celebrated on November 1, and is a day for honoring saints and the recently departed.

The traditions came to include practices to ward off spirits and honor the dead in European countries. The British believed fire warded off evil spirits, so churches bought extra dandles and held bonfires in graveyards. The Spanish visited graveyards and consecrated graves with holy water or milk. French monks took a less superstitious action on the day, sending prayers to saints, according "Halloween: From Pagan Ritual to Party Night."

The Irish, however, were really the first to start the tradition of trick-or-treating. Halloween reached America in the mid-19th century with the influx of Irish immigrants who brought their mix of Samhain, Pomona and pagan traditions.

Although the holiday clearly is derived from the Church, Halloween has always been a sensitive subject in terms of religion. Some have argued Halloween is a ritual for devil worship, trying to find evidence of animal or human sacrifice in ancient traditions associated with the holiday.  However, the Christian Coalition declared in 1982 that Hallowmass or Samhain were not "satanic rituals."

Today, the holiday has influence on many different countries around the world.

Because of the French Catholic Church's strong campaign against Halloween, the French did not celebrate the holiday until the mid-1990s, but today, for their "La Fete D'Halloween," people go from store to store collecting candy, not from house to house. Children will sometimes ask for flowers or money to decorate tombstones.

Germans celebrate, or rather, protect themselves from Halloween by hiding all the knives in their houses, in case spirits with old grudges return to cause trouble.

Swedish students get a full week off for Halloween, or what they call "Alla Helgons," and adults have shorter workdays.

Of course, many countries with a strong Catholic influence, such as Mexico, celebrate the holiday closer to how the Ancients did, with visits to cemeteries to bless the graves and send prayers, according to "The Halloween Handbook" (Citadel, 2001).