When you really think about it, many holiday traditions are bizarre. Who decided kids should start putting on costumes and going from door to door asking for candy on Halloween? What is Halloween anyway?

The question is tough to answer because the Halloween we celebrate in America today seems to be a blend of traditions from a variety of cultures. There is little historical documentation that can tell us when and why these traditions started, but there is a general consensus about the origins of some of our customs.

According to an article in American Heritage Magazine by Ellen Feldman, Oct. 31 was the last day of the year for the ancient Celts. It marked the beginning of the festival of Samhain, the end of the harvest, and the beginning of a long, cold, dark winter. On this night, it was believed that the spirits of the dead returned to roam the land. These spirits were thought to have done everything from foretelling future marriages to destroying crops and causing illness. Some people set out food and drink to welcome the spirits, while others put candles in hollowed-out turnips to ward them away. Villagers also built bonfires to burn animal remains and sacrifices to the gods.

By the 1st century A.D., the Romans had conquered much of Europe. The Roman celebration of Pomona, a goddess of fruit who was represented by an apple, was blended with Samhain. It is speculated that the old tradition of bobbing for apples may have come from Roman influence.

When Christianity began to spread throughout Europe, the church made an effort to convert the Celtic people, but had a tough time getting them to give up the Samhain celebration. So, in the 8th century, Pope Gregory III moved All Saints' Day, also known as All Hallows, from May 13 to Nov. 1 and Oct. 31 became known as All Hallows' Eve, Hallow Even, or Hallowe'en. This way, the Celts could continue to celebrate their departed loved ones, as long as they also celebrated the saints and prayed for their own immortal souls. It was during this time that the tradition of “souling,” going from door to door praying for the dead in exchange for food, began in the British Isles.

As the church spread its influence throughout Europe and beyond, Halloween became a more widely recognized celebration. Then came the Protestant Reformation, which did away with All Saints' Day and Halloween. The British found a way to keep having church-sanctioned fun; however, by moving the traditional Halloween festivities to Nov. 5, Guy Fawkes Day, to commemorate the day on which a plot by Catholic activists to blow up the Houses of Parliament was foiled.

When European powers began colonizing North America, their customs changed and adapted. In Mexico, All Saints' Day and All Souls' Day, as well as the night of Oct. 31, became the Day of the Dead or Days of the Dead. According to an article by Stanley Brandes from the Journal of American Folklore, Mexicans celebrated by visiting the graves of loved ones and by making figures of skulls and skeletons out of sugar paste. While many Mexican Catholics, as well as Catholics around the world, still attend Mass on these days, the colorful festivities of Day of the Dead are unique to Mexico.

The strict Puritans of New England didn't even celebrate Christmas, let alone Halloween, but some Catholics in America still observed All Hallows' Eve, and colonists continued to throw parties and light bonfires on Guy Fawkes Day. Americans maintained an interest in the occult, and the beginning of autumn remained a time for ghost stories and fortune telling. However, most Americans did not recognize Halloween until Irish and Scottish immigrants began to arrive by the thousands in the 1800s. Instead of turnips, Halloween revelers began hollowing out pumpkins and carving faces into them.

It wasn't until some time in the 1920s or 1930s that the tradition of “souling” evolved into the American tradition of “trick-or-treating.” It's difficult to tell how that evolution came about, but it's safe to say that trick-or-treating paved the way for business to begin capitalizing on the holiday. Today, Americans spend about six million dollars on Halloween costumes, candy, and decorations. The only holiday Americans spend more on is Christmas.

Somehow, an ancient Celtic festival survived Roman invasion, Catholic influence, Protestant reformation, and immigration to become, over a thousand years later, a day when kids can put on costumes and get free candy. While it may have become commercialized like so many holidays in the United States, it's really a centuries-old tradition, an expression of the timeless desire to throw one last party before the long winter.