The festival would see people light bonfires and wear costumes to ward off ghosts.

In the eighth century, Pope Gregory III designated November 1 as a time to honour all saints.

Soon, All Saints Day incorporated some of the traditions of Samhain. 

The evening before was known as All Hallows Eve, and later Halloween.

Celtic tales are full of mystical creatures like fairies, demons and pagan gods, often with evil or magical powers.

Many historians believe they are the origin of Halloween's more sinister side.

According to the New York Library, while Halloween originated in Europe, the holiday became the celebration it is recognised today as when it was brought to America by the early settlers. 

The original jack-o'-lanterns were carved out turnips filled with candles which were later switched to pumpkins by Americans. 

Over time, Halloween evolved into what it is known for today. 

Why has Halloween grown in Australia?

Lauren Rosewarne, an associate professor at the University of Melbourne, said social media and Hollywood have played a major role in Halloween's growth in Australia. 

"Social media of course, is a vehicle for people to share photos and videos of things like costumes and house decorations, thus increasing the present of the holiday in our lives and potentially motivating some people to want to get involved themselves," she said. 

"For a long time we've seen this all play out in the US but Australians have taken much longer to embrace it. 

"Now that there are more people participating, reluctant folks who don't want to be the only house in the street with fake cobwebs, now feel a little bit more emboldened to participate."

Spokesperson for the Australian Retailers Association (ARA) Paul Zahra said Halloween has become a significant retail event in Australia in recent years. 

"The average spend for Halloween in Australia is $93 per person," he said. 

"It is down on last year based on cost of living pressures households are under, but in saying that, it has been the fastest growing retail event in the past five years.

"It has taken a while for it to be embedded but certainly that is the case today."

He agreed that the visibility of Halloween with American brands and social media has encouraged demand too. 

"Halloween, Black Friday promotions have grown here because of the internet, so people can see what's happening internationally and that's why we're seeing the homogenisation of retail as a global trend."

Australians stocking up on Halloween items

Mr Zahra said access to everyday-people on social media marking the holiday has shown you can spend as little or as much as you want. 

"We expect people to spend less but we see more people looking at creative, budget conscious ways of creating costumes and celebrating."

According to ARA data, this year 38 per cent of Australians will stock up on lollies for trick or treaters, 37 per cent will also be buying Halloween costumes, and 32 per cent will be buying home decor.

Even Australian growers are set to cash in on Halloween, with over 1 million kilograms of pumpkins set to be sold. 

"Many retailers are well poised to take advantage of those opportunities."

Ellen Garbarino, a professor in consumer marketing at the University of Sydney, agrees the market for Halloween items is being responsive to demand. 

"I think the market is more responsive than driving it," she said. 

"People are not buying a costume because they've seen it in a store and think they have to, they're buying it because they want to party or go trick or treating."

So why has popularity of Halloween grown in Australia?

Born in America, Professor Garabino's home on her suburban Sydney street is known as the "Halloween house" and was the only one decorated when her family moved in over a decade ago. 

Now the entire street joins in for what she said is a uniquely community-focused event on the calendar. 

"To me it is the only community holiday where it only really works if strangers participate in a shared activity at the same time on the same day," she said. 

"There's a social contract about it, kids dress up and wander down the street and knock on doors of strangers and get candy.

"It adheres a script on what happens, and it builds familiarity in the community."

She said, in Australia celebrations are more about socialisation than being "scary". 

"That is partly because it's daylight savings in spring here so the scary vibe doesn't work as well at five in the afternoon on a sunny day."

But it's not just children getting into the spirit.

While some are likely parents, the ARA has found the largest cohort of people celebrating Halloween in Australia are 35-59 year olds, followed by under 35s. 

"I think it feeds our need to celebrate, feel a socially sanctioned way to be different and break out of our normal constraints.

"To say, 'Hey, I usually dress boring but tonight I'm going to dress as a sexy nurse.'"

'A bit of fun'

Dr Rosewarne believes there will always be some opposed to celebrating Halloween and a "supposed American encroachment on the 'Australian way of life'". 

"For others — particularly those with young children who embrace the opportunity to dress-up — this will be an opportunity to have fun, to be a bit silly and to hang around with friends. 

"Sure, it has strong commercial components but very little in our culture exists as separate from consumerism."