Tonight being Hallowe'en, revellers of all ages will be disguising themselves in weird and wonderful costumes and celebrating in various ways. Children will go door-to-door trick-or-treating, while adults will gather for house parties or haunt the night spots.

Few will give a thought to how this annual night of 'haunted' houses, witches and goblins, ghosts and ghouls, evolved, or even how some of today's established customs began. One thing is certain: Hallowe'en as it is celebrated today is nothing like its origins.

The term 'hallowe'en' is a shortened version of All-Hallow-Even — the eve of All Hallows' Day, now known as All Saints Day, which is celebrated on November 1.

Hallowe'en originated in Ireland from the pagan festival 'Samhain' (pronounced SOW-ain), and was one of four "fire" festivals of the pre-Christian Celtic calendar year marking the end of the harvest season in Gaelic culture.

In the old terminology of the times 'pagan' was not associated with the devil; rather it was an unflattering reference used by the ruling classes to define unsophisticated country folk.

The Ancient Gaels believed that on October 31 the boundaries between the worlds of the living and the dead overlapped, and the deceased would come back to life, freely walking the Earth and causing havoc, such as sickness or damaged crops.

So large, communal bonfires were set, on which the bones of slaughtered livestock were thrown. The word 'bonfire' is said to derive from 'bone fire', and the belief was that bonfires and sacrifices guaranteed the sun would burn brightly after a long, dreary winter.

People dressed up in elaborate animal skins and heads the better to blend in with the evil spirits when out of doors. This gradually evolved into trick-or-treating because children would knock on their neighbours' doors in order to gather fruit, nuts and candies for the Hallowe'en festival.

Houses were frequently decorated with pumpkins or turnips carved into scary faces and illuminated with a candle for an eerie effect.

With a shared Gaelic culture and language, Scotland has also celebrated Samhaim enthusiastically for centuries, and Robert Burns portrayed the varied customs in his 1785 poem, 'Hallowe'en'.

Hallowe'en arrived in America in the 19th century, thanks to the migration of nearly two million Irish following the great potato famine of 1845-49. Scottish emigration from the British Isles, primarily to Canada before 1870, and to the US thereafter, brought the Scottish version of the holiday to each country.

The commercialisation of Hallowe'en in the US began in the 20th century, with mass-produced costumes first appearing in the stores in the 1930s. The custom of trick-or-treating became an established fixture of the celebration in the 1950s.

Pumpkins replaced turnips in the US for jack-o-lanterns because they were easier to carve. The term 'jack-o-lantern' originates with the Celts. It is said that a nasty man named Jack once tricked the devil, as a result of which he was denied entry to heaven or hell after death, instead condemned to roaming the earth ceaselessly. To ward off evil spirits Jack made a lantern out of a carved turnip, in which he placed a lump of lighted coal.

Orange and black are the colours which are synonymous with Hallowe'en — orange because it is associated with the autumn harvest, and black with darkness and death.

Black cats were once believed to be witches' familiars who protected their powers, while vampires are mythical beings who defy death by sucking human blood. Vampire bats are not from Transylvania but Central and South America, where they feed on the blood of birds, horses and cattle.

Thanks to aggressive promotion by the United States, where Hallowe'en has become the second most commercially successful holiday after Christmas, many countries around the world also now celebrate the date in style.

Whereas once it was children and adults, in homemade costumes, who marked the event, today it is a multi-billion dollar industry, with everything from themed candy to interior and exterior decorations, party ware, CDs and more, being touted as "a must". Indeed, it is estimated that annual sales of Hallowe'en candy alone total around $2 billion.

Unfortunately, vandalism and hooliganism continue to plague what was once innocent fun in many countries, often stretching Police services to the maximum, and resulting in serious injury or death to revellers. As a result, some of the long-established traditions are being dropped in favour of "safe" parties in homes, church and school halls, but the spirit of Hallowe'en remains intact.