One of the oldest Halloween traditions comes from the ancient Celts， who lived in western and central Europe long ago. The Celts celebrated a holiday called Samhain on October 31. After sunset that day， people believed that spirits of the dead would rise and walk the earth. The Celts made offerings of food and drink to keep the spirits away.
Beginning about 2，000 years ago， the Roman Empire conquered many Celtic peoples. But Celtic traditions， including Samhain， remained strong in areas such as Ireland and Scotland， even after the Roman conquest.
The Roman Catholic Church tried to replace Samhain in 835 with All Saints' Day， a day to honor saints of the Church. The eve of All Saints' Day is October 31. It is called Allhallows or Hallowmas by the Church.精彩内容，尽在百度攻略：http://gl.baidu.com