(Painting: "The Fairy Festival" by Gustave Doré
Taken from http://www.victorianweb.org/painting/dore/wc/1.html)
Ireland, the green land of dreams, is considered the motherland of Little Folk. Celtic nations describe them as a race of diminutive people who had been driven into hiding by invading humans. They came to be seen as another race, or possibly spirits, and are believed to live in an Otherworld, in hidden hills and burial mounds, or across the Western Sea. The Otherworld realms include Mag Mell (the Pleasant Plain), Emain Ablach (the Fortress of Apples or the Land of Promise or the Isle of Women), and Tir na nÓg (the Land of Youth).
Another theory is that Faeries were originally worshiped as goddesses and gods, spirits of nature, but with the coming of Christianity these beliefs were disappearing. They lived on, in a dwindled state of power, in folk belief.
With Christianity the perception of Fair Folk creatures was changed, and sometimes all Faeries, good or malicious, helpful or dangerous, came to be indistinguishable from devils, were viewed with superstition and blamed for all that went wrong: sour milk, failed crops, difficult character of the child, drowning and deaths from the unknown diseases. The time went by, anyway, and some of the few traditions and beliefs survived, others were modified and adapted to the actual period, yet many have been forgotten. The continuous development of the industrial society, the decreasing consciousness of damages caused to nature, the growth of the consumerism at a loss of the spiritual values and traditions – all that makes Fair Folk avoid people, hide, escape and gradually disappear from our world.