According to tradition, St. Patrick himself founded this religious community in the fifth century, appointing Dabheoc as its first abbot. The monastery eventually became a priory under the Augustinian Abbey of SS Peter and Paul in Armagh during the 1130s, before being abandoned at the close of the sixteenth century. Its primary purpose was to serve the countless pilgrims who journeyed to St. Patrick’s Purgatory, a cave that drew visitors from across medieval Europe and inspired a wealth of literature about the site.

The archaeological remains on Saint’s Island tell the story of centuries of religious activity. The western half of an earthen enclosure, roughly 20 metres in diameter with an outer fosse, marks the earliest settlement. At the heart of the island sits a rectangular graveyard, enclosed by drystone walls and measuring 27 by 22.5 metres, its interior scattered with graveslabs placed atop mounds of rubble. A 44-metre pathway, defined by two parallel lines of grass-covered stones, leads to the foundations of another rectangular structure, built from drystone with walls nearly a metre high. Additional features include what appears to be part of a circular enclosure to the northeast and traces of an old quay where pilgrims once landed.

The pilgrimage route itself reveals the significance of this sacred landscape. An ancient roadway from Pettigo village passes by Rathnacross ringfort and Templecarn church and burial ground before reaching the southwest shore of the lake, where a wooden bridge once connected the mainland to Saint’s Island. Natural boulders jutting from the water may be all that remain of this crossing. Around the lake, other religious sites add to the area’s spiritual geography; St. Brigid’s Chair, a naturally formed L-shaped stone, sits on the southeast shore, whilst St. Dabheoc’s Seat, once featuring a stone seat before a grave-like opening on a southern hill, has since been lost to forest growth.