Imagine this: people in 4th Century Europe devoting a day to pray for the many martyrs and saints who have fallen. Now imagine this: children shivering as they make their way door to door in creative, silly costumes asking for candy. How exactly did this transition occur?

Halloween is often regarded as a Pagan holiday, but this ghoulish holiday actually finds its deepest roots in Christianity. In fact, Halloween's history links back to another holiday, All Saints' Day.

"It (All Saints' Day celebrations) started as something Christians were just doing ... and as it became more popular, it spread," said James Felak, UW associate professor of history. "Certainly by the 4th Century it became a common practice to honor the martyrs."

As common as the practice was, it would take centuries before the holiday became official.

"By the 11th Century, Pope Gregory VII declared Nov. 1 as the official date for the holiday, although it started out with no link to Halloween in terms of wearing masks," Felak said.

In English, the celebration was called All Hallow's Eve, with hallow meaning 'saints' and therefore, all holy ones.

But these celebrations were more than your average vigil; this is where the spookiness of Halloween might have originated.

"One of the most interesting aspects of it is that they would take the relic of a saint, something they have, whole skeletons, teeth, and you can go see it [on display]," Felak said.

But as eerie as this may seem, this practice was and is still in practice.

"Body parts of saints were highly revered; bones were everywhere. Any catholic church with any respectability sought to have body parts of deceased saints," said James Green, UW professor of anthropology. "I've seen what are called relic quarries. I didn't see any bones where bones were allegedly there, but it didn't make a difference to people how much of a body part there was; it could be a toenail. St. Anthony's tongue was preserved and people were on their knees praying to the tongue."

But, in fact, these relics and the relic quarries that they were stored in were more than just a symbol of faith.

"It was believed that it was almost a trade network; having a relic in a shrine or cathedral was one of the things you could have to assure pilgrims came to your city. This meant commercial opportunities for locals," Green said.

Similarly, Halloween as it is commonly celebrated today, also finds its influences in commercial interests.

"I do know that in this country during the mid-to-late 19th Century, holidays were being commercialized," Green said. "Christmas and Halloween in particular became important to toy and candy manufacturers."

Although loosely linked with All Saints' Day, it was actually manufacturers who transformed this Christian holiday to what has now become a socio-cultural holiday. But manufacturers alone weren't the players to influence this modern holiday.

"The reason was also in part due to the industrial revolution," Green said.

Green said with the growing middle-class' discretionary money came an increase in emphasis on domesticity. These things emerged out in part from the industrial revolution creating a middle class and thus middle class holidays substituted for older, religiously inspired ones.

With the notion of family deeply rooted into society, Halloween soon became what we know it as today: a holiday for all.

"As holidays became more commercialized, more domesticated, families became more associated with little kids going door-to-door getting treats," Green said.

Yet, there was a time when "trick-or-treat" was more than just a harmless greeting.

"The business of going door-to-door and threatening to do damage, where it comes from is 17th and early 18th century practices of New Year's in this country," Green said.

Green said Christmas in the 1700s went on for a week and climaxed at New Year's. It involved a lot of drinking and rowdiness; people of the working classes would go door to door to the homes of the rich, demanding food and drinks.

In fact, even until quite recently, the notion of harmful trick-or-treating was still in practice.

"When I was a kid, these people really did do damage," Green recalled. "Halloween was an occasion where people trampled houses or shot out street lights with BB guns, just general vandalism was occurring."

Fortunately, trick-or-treating has left its harmful roots behind and established itself as the core of Halloween festivities. However, there are varying opinions about the celebration of Halloween.

"For us catholics, we're not opposed to Halloween," said Father Garry Cappleman, O.P. (Order of Preachers) of the Newman Catholic Center. "We see Halloween as a kid going to celebrate and we celebrate Halloween because for us it's make-believe. Witches, ghosts and goblins are more of a fun thing that we don't take seriously."

What would those 4th century villagers think when they learn that their sacred holiday has evolved into a night of festivities? There are dozens of other Halloween traditions that may in fact have intriguing origins, but when it boils down to it, All Saints' Day has influenced the way in which Halloween is viewed and celebrated today.