Even after Christianity was made the vital religion in Ireland, it was believed that places not exorcised by prayers and by the sign of the cross, were still haunted by Druids. As late as the fifth century the Druids kept their skill in fortune-telling. King Dathi got a Druid to foretell what would happen to him from one Hallowe'en to the next, and the prophecy came true. Their religion was now declared evil, and all evil or at any rate suspicious beings were assigned to them or to the devil as followers. "_Maire Bruin:_ Are not they, likewise, the children of God? _Father Hart:_ Colleen, they are the children of the fiend, And they have power until the end of Time, When God shall fight with them a great pitched battle And hack them into pieces." YEATS: _Land of Heart's Desire._ The power of fairy music was so great that St. Patrick himself was put to sleep by a minstrel who appeared to him on the day before Samhain. The Tuatha De Danann, angered at the renegade people who no longer did them honor, sent another minstrel, who after laying the ancient religious seat Tara under a twenty-three years' charm, burned up the city with his fiery breath. These infamous spirits dwelt in grassy mounds, called "forts," which were the entrances to underground palaces full of treasure, where was always music and dancing. These treasure-houses were open only on November Eve "For the fairy mounds of Erinn are always opened about Hallowe'en." _Expedition of Nera._ (Meyer _trans._) when the throngs of spirits, fairies, and goblins trooped out for revels about the country. The old Druid idea of obsession, the besieging of a person by an evil spirit, was practised by them at that time. "This is the first day of the winter, and to-day the Hosts of the Air are in their greatest power." WARREN: _Twig of Thorn._ If the fairies wished to seize a mortal--which power they had as the sun-god could take men to himself--they caused him to give them certain tokens by which he delivered himself into their hands. They might be milk and fire-- "_Maire Bruin:_ A little queer old woman cloaked in green, Who came to beg a porringer of milk. _Bridget Bruin:_ The good people go asking milk and fire Upon May Eve--woe to the house that gives, For they have power over it for a year." YEATS: _Land of Heart's Desire._ or one might receive a fairy thorn such as Oonah brings home, which shrivels up at the touch of St. Bridget's image; "Oh, ever since I kept the twig of thorn and hid it, I have seen strange things, and heard strange laughter and far voices calling." WARREN: _Twig of Thorn._