Souterrain, Lisnenan, Co. Donegal

Located just 60 metres from a known cashel and 370 metres from a holy well, this underground passage had remained hidden beneath the Donegal countryside until September 2006. Though no archaeological conditions had been placed on the development, the construction company promptly reported their find to the authorities, and archaeologist Declan Moore was brought in to record the structure before building work continued.

The souterrain, a type of underground chamber commonly built in Ireland during the early medieval period, had suffered considerable damage by the time archaeologists arrived. The stone lined passage curved for approximately five metres from east to west, following the natural slope of the hillside. Its walls, built from a single layer of stones ranging from small 100mm pieces to substantial 500mm blocks, survived up to nine courses high in places, reaching a maximum depth of 1.45 metres. The builders had used a clever construction technique, placing smaller stones in the upper courses whilst using much larger blocks as the foundation, with occasional slate pieces and daub filling the gaps.

What remained of the entrance lay at the western, downhill end of the passage, appearing as a roughly rectangular pit that formed a small court area. Though the site had been heavily disturbed and all the capstones that would have roofed the structure had been displaced, archaeologists could still trace the original cut into the hillside and document how this hidden chamber had been carefully constructed. The absence of any other archaeological material suggests this souterrain stood alone on the slope, perhaps serving as a refuge or storage space for the inhabitants of the nearby cashel centuries ago.