To commemorate the night, they built large bonfires and made animal and crop sacrifices in an attempt to appease the god. At the end of the evening each took a torch lit with the flames from the bonfire home to light their hearth fires to protect them during the winter months. Some feel the significance of candles and lights on Halloween stems from this tradition.
In later years, with the influence of Christianity, October 31 came to be known as All Hallows Eve. November 1 is a day of observance called All Hallows Day (better known as "All Saints Day") where saints, martyrs and those who have passed before us are honoured. October 31 eventually adopted the official name of Halloween years later.
The modern tradition of "trick or treating" dates back to early times in England and "All Soul's Day" parades. During the parades, poor citizens would beg for food and families would hand out "soul cakes" in exchange for prayers for dead relatives. Later, children would simply go house to house looking for food, money and ale. If you refused to hand out something, evil spirits would descend on your home. It is thought that Irish immigrants brought this tradition to the Americas in the early 1800's.
Costuming originated from the Celtic tradition of dressing as animals and wearing masks around the bonfire to appease the god of the dead. Later, people began to wear masks hoping to disguise themselves from the ghosts and goblins that roamed on Hallows Eve. Today it has expanded to include a wide variety of spooky creatures, animals, action figures and many more creative ideas.