About 2000 years ago, the Celts celebrated their new year ( Samhain) on November 1st, marking the end of summer. The Celts believed that on the eve of the new year, the dead would join the living and bring with them comfort and direction for the Druids (Celtic Priests).
The Druids built bonfires, where sacrifices were offered to their deities. The Celts wore costumes made out of animal heads and skins, and told each other's fortunes.
In the 7th century Pope Boniface IV designated November 1st as All Saints' Day,
trying to replace the Celtic Festival with a church-sanctioned holiday. In 1000 AD
the church made November 2nd into All Souls' Day to honor the dead. Celebrations of this holiday were similar to Samhain - bonfires, parades and dressing up as angels and demons. The
"Eve of All Saints" and "All Souls" were called "Hallowmas".
The tradition of wearing masks and scary costumes came from the fear of being recognized by the ghosts that walked among the living during Hallowmas. To keep ghosts away from homes, bowls of food were placed outside to appease the spirits.
Later, various Halloween customs emerged in America, as European immigrants arrived.
The first celebrations included parties and public events, where stories of the dead were shared, fortunes were told, dancing, singing, and tricks also were part of this holiday.
It was not until the middle of the 19th Century, when millions of Irish immigrants arrived in America, that the celebration of Hallowmas became popular in a national sense. In the US. in the late 1800's, Americans were encouraged to mold the holiday into one that was celebrated without anything frightening, superstitious or with religious overtones.
Between the 1920's and 1950's, trick-or-treating was revived. Since vandalism
had plagued Halloween celebrations, families began providing neighborhood children with treats to prevent tricks being played on them.