Fairy forts (also known as raths from the Irish, referring to an earthen mound) are the remains of lios (ringforts), hillforts or other circular dwellings in Ireland. From (possibly) late Iron Age to early Christian times, the island's occupants built circular structures with earth banks or ditches. These were sometimes topped with wooden palisades, and wooden framed buildings. As the dwellings were not durable, in many cases only vague circular marks remain in the landscape.Raths and lios are found in all parts of Ireland.
Tradition claimed that ringforts were "fairy forts" imbued with Druids' magic and believers in the fairies did not alter them. The early pre-Celtic inhabitants of Ireland (known as the Tuatha Dé Danann and Fir Bolg) came to be seen as mythical and were associated with stories of fairies, also known as the "Good People". Fairy forts and prehistoric Tumuli were seen as entrances to their world. Even cutting brush, especially the sceach or whitethorn, on fairy forts was reputed to be the death of those who performed the act.
There are many folk tales about supernatural events happening at fairy forts. Real accidents which happened at ringforts could be given supernatural explanations. For example, a man who tried to blast a dolmen suffered a septic hand. The wrecked dolmen was subsequently left untouched.
Other traditions hold that a leprechaun may allegedly know of hidden gold in a fairy fort.
In literature, British author Rudyard Kipling made allusions to the process by which such legends grow in his 1906 novel, Puck of Pook's Hill.
Workmen were working to level earthworks in a fairy fort at Dooneeva. The originator of this fell apparently dead. His wife, a wise woman brought him back to life magically.
A farmer's best cow kept grazing in a fairy fort. It was unlucky for the cow to graze there but the cow pined when it was prevented from going to the fairy fort. One day the farmer found the cow there with broken legs. He killed the cow and his family ate the meat, some fresh and some salted. A year later the cow was seen in the fairy fort. The fairies told the farmer they had taken the cow because they needed the milk for their children. They had substituted an old stray horse and made the horse to be like the cow. The farmer took his cow home. He became very prosperous because the fairies supported him.