Fairy fort

Fairy forts (also known as lios or raths from the Irish, referring to an earthen mound) are the remains of stone circles, ringforts, hillforts, or other circular prehistoric dwellings in Ireland. From (possibly) the 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, only vague circular marks often remained in the landscape. The remains of these structures, in conjunction with the vegetation around them, are associated with local traditions and folklore, perhaps involving fairies or other supposed supernatural entities, who would "defend" the structures from destruction by builders or farmers.

As of 1991, there were between thirty and forty thousand identifiable fairy forts in Ireland's countryside, the oldest of them possibly dating back as early as 600 BCE.