Halloween has roots in the Celtic festival of Samhain [pronounced: sow- wen] and the Christian holy day of All Saints’ Day.
The ancient Celts believed that on October 31st the boundary between this world and the otherworld dissolved, and the dead become dangerous for the living by causing problems. The tradition of costumes and masks being worn at Halloween goes back to the Celtic traditions of attempting to copy the evil spirits or pacify them.
The name Halloween is from, "All Hallows' Evening", since it is the eve of "All Hallows’ Day", which is now also known as All Saints' Day. Halloween is thought of as a time when the living and the dead can be together again.
On All Hallows’ Eve, the ancient Celts would place a skeleton on their windowsill to represent the departed. Lanterns were first carved from a turnip or rutabaga. Believing that the head was the most powerful part of the body, containing the spirit and the knowledge, the Celts used the "head" of the vegetable to frighten off the embodiment of superstitions.
The name jack-o'-lantern can be traced back to the Irish legend of Stingy Jack, a greedy, gambling, hard-drinking old farmer. He tricked the devil into climbing a tree and trapped him by carving a cross into the tree trunk. In revenge, the devil placed a curse on Jack, condemning him to forever wander the earth at night with the only light he had: a candle inside of a hollowed turnip.
The carving of pumpkins in North America came about because pumpkins are both readily available and easier to carve than turnips.
Today being the 13th, I thought, it'd be a grand day to start the lead up.
A few events that occurred October 13th in History:
54 - Claudius, the forth Roman Emperor of the Julio-Claudian dynasty, dies.
54 – Nero, the fifth and last Roman emperor of the Julio-Claudian dynasty, ascends to the Roman throne. An early persecutor of Christians, the First Roman-Jewish War (66–70) started during his reign. Later, facing assassination, Nero commited suicide.
1244 – Jaques de Molay, Grand Master of the Knights Templar is born.
1307 – Hundreds of Knights Templar in France are simultaneously arrested by agents of Phillip the Fair, to be later tortured into "admitting" heresy. (The actual day was Friday the 13th)
1582 – Because of the implementation of the Gregorian calendar, this day does not exist in this year in Italy, Poland, Portugal and Spain.
1892 – Edward Emerson Barnard discovers D/1892 T1, the first comet discovered by photographic means, on the night of October 13-14.
1917 - The "Miracle of the Sun" is witnessed by an estimated 70,000 people in the Cova da Iria in Fátima, Portugal.
1943 – World War II: The new government of Italy sides with the Allies and declares war on Germany.
1958 - The first of a series of books featuring Paddington Bear is published "A Bear Called Paddington" , the first story is about a bear who is found at Paddington railway station in London by the Brown family.
1972 - Uruguayan Air Force Flight 571 crashes in the Andes mountains. Survivors had to resort cannibalism. 16 of the original 45 passengers survived the ordeal.
2008 - After suffering a meltdown in the markets in the preceeding weeks with the Dow Jones Industrial Average falling below 7900 markets rally with a gain of 936 points, its highest ever one day gain.
Much of the above information was taken from Wikipedia.