I wasn't really sure of the historical details associated with this, but then Wikipedia gives it all. In a nutshell,
The modern holiday of Halloween has its origins in the ancient Gaelic festival known as Samhain (pronounced /ˈsˠaunʲ/ from the Old Irish samain). The festival of Samhain is a celebration of the end of the harvest season in Gaelic culture, and is sometimes erroneously regarded as the "Celtic New Year". Traditionally, the festival was a time used by the ancient pagans to take stock of supplies and slaughter livestock for winter stores. 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 and cause havoc such as sickness or damaged crops. The festivals would frequently involve bonfires, where the bones of slaughtered livestock were thrown. Costumes and masks were also worn at the festivals in an attempt to mimic the evil spirits or placate them. When the Romans occupied Celtic territory, several Roman traditions were also incorporated into the festivals. Feralia, a day celebrated in late October by the Romans for the passing of the dead as well as a festival which celebrated the Roman Goddess Pomona, the goddess of fruit were incorporated into the celebrations. The symbol of Pomona was an apple, which is a proposed origin for the tradition of bobbing for apples on Halloween.
Enough of enlightening and as the saying goes, a picture says more than a throusand words.
P.S: There was this hilarious incident where a genuine fire brigade was rushing to some spot, and a seemingly moron chap with an axe and dressed up started sprinting behind it. To add to the hysteria, once he was done, an encore chanting 'Bravo' went up. Crazy Austin, but its fun.