People will often tell you that Halloween was, once upon a time, a pagan holiday from Celtic culture. In fact the way the ancient Celts celebrated the end of October was quite drastically different. So how did sacrificing goats and dancing around a bonfire turn into candy, kids and zombies?
Once upon a time...
Around the year 43 AD, the Roman Empire landed on the shores of what is now Britain and very quickly took over. For 400 years they ruled, slowly encroaching on the Celt's territory and trying to brainwash them into the Roman way of life. They attempted to blend Celtic traditions with their own festivities, most notably Feralia - a holiday celebrating the dead - and Pomona's Day of Honoring, where they honored the goddess of fruit and trees, Pomona (which could explain the beginnings of bobbing for apples).
When church bells ring
Next, around 800 AD, came the Church. In his own way of civilizing the Celts, Pope Boniface IV created Christian holidays around this same time of year, October 31 being declared All Hallows Eve and November 1 as All Saints Day.
Christianizing the Celtic people continued over the next few hundred years, and November 2 was declared All Soul's Day - together making the three-day holiday of Hallowmas to replace the pagan festival.
So you see, though it started with the Celtic dead, foreign powers slowly wiped out ancient traditions in place of their own. However, the veil between our world and the next still thins around this time of year no matter what you believe - so if you'd like to take advantage, book a Lantern Ghost Tours paranormal investigation and attempt to communicate with the dead … if you can stomach what they have to say.