At Magheraboy in County Mayo, local tradition holds that somewhere beneath the interior of a rath lies a souterrain, an underground stone-lined passage of the kind that early medieval farming communities built for storage, refuge, or both. No opening, no depression, no tell-tale scatter of disturbed earth marks the spot. Whatever lies below, if anything does, the ground above it gives nothing away.

The rath itself, a ringfort enclosed by an earthen bank and ditch, is the kind of settlement that tens of thousands of Irish families occupied between roughly the sixth and twelfth centuries. Souterrains were often dug within or beside such enclosures, their narrow passages and corbelled chambers sealed just below the turf. Many have been found by accident, when farm machinery breaks through a roof slab or a field drains unexpectedly. At Magheraboy, no such accident has yet confirmed what local memory has apparently preserved. The tradition of a souterrain here has been passed down without any corresponding physical evidence emerging at ground surface, which places it in an interesting category: a piece of inherited knowledge that archaeology has neither proved nor disproved.