People have been celebrating Halloween—or some version of it—for more than 2,000 years. Today, many mistakenly associate this Americanized holiday with Dia de los Muertos (Day of the Dead). However, that is not quite true. The roots of Halloween reach much farther back, to Western Europe B.C.E.

The Original Halloween

Halloween originates from the Celtic New Year festival, Samhain (sow-in). The Celts, who lived during the Iron Age in the areas that are now Ireland, the U.K., and parts of northern Europe, celebrated their New Year on November 1. The Celts split their years into two halves—light and dark. Literally meaning “summer’s end” in modern Irish, Samhain marked the end of the light half of the year and the beginning of the dark half. This day signaled both a time of rebirth (a bountiful harvest) and death (a harsh winter).

Along with ushering in a new year, this was a time for the Celts to take stock and make sacrifices. They believed that on New Year’s Eve, the “world of the gods” was made visible to humankind. This open border allowed otherworldly spirits to enter the natural world. Faeries would play tricks, ghosts of the dead would visit the living, and the gods would cause trouble. However, they also believed that the presence of these spirits could provide the Celtic priests a clearer sight. The Druid priests recited prophecies and made predictions about the future.

Sacred bonfires were built to commemorate this event. Here, Druids sacrificed crops and animals to appease the Celtic deities. People gathered around the fire dressed in costumes of animal heads and skins in hopes of fooling spirits who might want to harm them on this night. Likewise, they left offerings outside of their homes to deter the devious faeries. The next day, using hollowed out turnips, the Celts would carry home a bit of the bonfire to light their own hearths and begin a new year.

These Celtic customs held strong for centuries until other visitors came to call.

Roman Influences

The Romans conquered most of the Celtic lands by 43 C.E., and ruled for nearly 400 years. Celtic customs and religion continued on through the Romans’ reign. They still held festivals in celebration of the equinoxes and solstices; Samhain was still observed on the night that the spirits come to visit. In the course of that time, Roman traditions began to meld with the Celtic. Two Roman holidays—Feralia and Pomona—were combined with the Celts’ celebration of Samhain.

Feralia was a day in late October for the Romans to commemorate the passing of the dead. The second holiday, observed at the end of the harvest, was a festival in honor of Pomona, the goddess of fruit and trees. The incorporation of Pomona’s symbol—an apple—into the Celtic festival is often thought to be the origins of the modern Halloween tradition of bobbing for apples.

Christianity Takes Over

Throughout the centuries of Roman sovereignty, Christianity grew. Emperors in the 4th century of the Common Era issued mandates making this religion more and more common. Even after the Empire fell in 476 C.E., Christianity continued to spread throughout Europe.

On May 13th, 609 C.E., Pope Boniface IV dedicated the Pantheon—formerly a Pagan temple—as a memorial to Christian martyrs. On this day, he established the Catholic feast of All Martyrs Day for the Western church. In the 8th century, Pope Gregory III expanded the festival to include saints, as well. In doing so, he moved the observance to November 1, and the celebration became known as All Saints’ Day.

By the 9th century, Christianity reached the Celtic lands, displacing Druidism and blending with Celtic rites.  The Catholic Church went on to establish November 2 as All Souls’. It is widely believed that All Souls’ Day was meant to replace the Celtic festival of the dead, in an attempt to dispel the ancient belief in faeries and monsters. But some things, like ghosts, don’t die.

The two Catholic holiday observations were similar to the Celtic Samhain celebrations. There were bonfires, feasts, parades, and costumes (though now they dressed up as saints, angels, and devils). The celebration on November 1 was often referred to as All-hallows, from Middle English Alholowmesse, meaning All Saints’ Day. October 31, the traditional night of Samhain, started to be known as All-hallows Eve and, eventually, Halloween.

Halloween in America

Early observations of Halloween could be sparsely seen in the colonial United States. Colonies south of Maryland were more likely to participate. The rigid Protestant belief systems that monopolized New England rejected anything that hinted of Catholicism. Soon a distinctly American version emerged from the blend of diverse groups on the land.  The first observances were community events to celebrate the harvest. Much like Samhain, neighbors would share stories of the dead, tell fortunes, dance and sing. Soon the telling of ghost stories and mischief-making were common around the harvest festivals.

Later on, in the late 19th century, large populations of Irish immigrated to the U.S. and brought with them their Halloween customs. This was the start of Halloween celebrations all across the nation. But the Great Depression and the World Wars kept participation at bay in the early 20th century. The 1950s is when Halloween’s popularity soared. Merchants began to realize that there was money to be made in manufacturing costumes and making candy. In fact, today, one quarter of the candy sold in the U.S. annually, is for Halloween.

According to the National Retail Federation in 2015, Halloween sales rose to nearly $7 billion yearly with 64% of Americans spending an average of $74.34 per person on candy, costumes, and decorations. It is now the second-largest commercial holiday in the country, only beat by Christmas.

Modern Traditions

If you were paying attention, it is easy to draw a line from modern American Halloween traditions to the ancient Celtic festival. Ghosts of the dead are still depicted today. Dressing up in costumes evolved from the cloaks of animal skins to ward off harmful spirits. Trick-or-Treating is an imitation of the Celtic leaving offerings outside of  their homes to dissuade trickery from faeries. And the hollowed out turnips carrying the sacred fire is the basis of Jack-O-Lanterns. After more than 2,000 years, celebrating Halloween seems to be as enduring as our innate fear of the dark and things that “go bump in the night,” or maybe we just can’t resist a feast to have fun and gorge on candy.