Halloween is a time of year people enjoy for many reasons - costumes, scary movies, sweet treats like toffee apples and more. Where does the day come from and why did we start celebrating it?This is what you need to know.Where does Halloween come from - and when is it?It’s believed that Halloween is descended from the festival of Samhain, a Gaelic celebration which marked the end of the harvest season and the beginning of winter, or the darker period of the year.People believed that it was during this time that the boundary between the world of the living and the world of the dead became blurred.A similar idea is also believed in regards to the Jewish holiday Yom Kippur, which also tends to occur in October and has people saying prayers for the dead.During the Samhain celebrations, great bonfires would be lit and loud drums would be played in order to guide visitors from the underworld. The Celts would wear costumes in order to ward off any malevolent spirits.With the influence of the Roman empire taking over Great Britain and much of Europe, the Samhain festival gradually got mixed in with the Roman celebrations of Feralia.The Feralia celebrations also honoured the dead, and Pomona, which paid tribute to the goddess of fruits and trees.Pope Gregory III, in the eighth century, declared 1 November to be a day on which all the saints and martyrs would be honoured, which came to be known as All Saints Day.The day before All Saints Day was known as All Hallows Eve, as hallows means a saint or a holy person, which later evolved into Allhalloween and then eventually Halloween.Halloween takes place every year on 31 October, and in 2021 it falls on a Sunday.When did we start celebrating Halloween?Much of what we know about modern day Halloween is a product of the Americanisation that the day has gone through over the years.It began with immigrants from Europe arriving in America and as different European ethnic groups and American Indians meshed, a new version of Halloween began to emerge.By the middle of the 19th century, yearly autumnal festivities were common, such as telling ghost stories and celebrating the harvest, but Halloween was not yet celebrated across the country.In the second half of the 19th century, a new wave of immigrants arrived in America, especially the millions from Ireland fleeing the Irish potato famine. It was these Irish immigrants that helped Halloween become a national celebration.What are some Halloween traditions?Many of our Halloween activities stem from old traditions - for example, while pumpkin carving began in America, it actually has Celtic roots.During Samhain, turnips would be used to make lanterns, and when the Irish arrived in America, they had to make do with pumpkins instead as there were no turnips to be found. Switching pumpkins for turnips has since made its way back to the UK.Additionally, “trick or treating” is an American term for a tradition that we already had in the UK.In the middle ages, “souling” was the British practice of going door to door and offering prayers for the dead in return for food.Similarly, since the 19th century, Scottish children have been going “guising”, which sees them dress as evil spirits in order to ward them off.The tradition of bobbing for apples can be traced back to the Roman holiday Pomona, which had an apple as its symbol. A version of this article originally appeared on NationalWorld.com