Samhain

Courtesy - Grimalkin Studio

In Celtic Ireland, Samhain (/ˈsɑːwɪn, ˈsaʊɪn/; Irish: [sˠəuɪnʲ]) marked the change from the lighter half of the year (summer) to the darker half (winter).  It was believed that during this time the division of this world from the otherworld was at it's thinnest, allowing spirits to pass through. "...time lost all meaning and the past, present, and future were one. The dead, and the denizens of the Other World, walked among the living. It was a time of fairies, ghosts, demons, and witches. Winter itself was the Season of Ghosts, and Samhain is the night of their release from the Underworld. Many people lit bonfires to keep the evil spirits at bay. Often a torch was lit and carried around the boundaries of the home and farm, to protect the property and residents against the spirits throughout the winter." [1]  Household fires were extinguished and then rekindled from the bonfire.

Two hills in the Boyne Valley were associated with the festivities. Tlachtga, the location of the Great Fire Festival, which was begun on the eve of Samhain (Halloween) and Tara.  Some Neolithic passage tombs in Ireland are aligned with the sunrise around the times of Samhain and Imbolc. These include the Mound of the Hostages(Dumha na nGiall) at the Hill of Tara,[12] and Cairn L at Slieve na Calliagh.[13]

Families honored their ancestors, inviting them home.  At the same time they tried to ward off harmful spirits by disguising themselves with costumes and masks.  Food was prepared for both the living and dead. The ancestral food was shared with the needy. 

With the coming of Christianity to Ireland, Samhain was incorporated with the feasts of All Saints (All Hallows) and All Souls at the beginning of November. The wearing of costumes and masks to ward off harmful spirits were incorporated into what became Halloween. 

In medieval Ireland the festival marked the end of the season for trade and warfare and was a time for tribal gatherings. These gatherings are a popular setting for early Irish tales.

The Irish brought their Halloween traditions to America where today it is a major celebration

• [1] Deeper into Samhain - Order of Bards, Ovates and Druids 
• Samhain Eve - by Damh the Bard mps 
• Samhain - The Celtic Roots of Halloween - New Grange . com
• Samhain - Wikipedia