A souterrain, to use the proper term, is an artificial tunnel or chamber built into the earth, usually during the early medieval period in Ireland, roughly between the seventh and twelfth centuries. They are found in their hundreds across the country, dug by hand and lined with drystone walling, their precise purposes still debated: cold storage, refuge, concealment, or some combination of all three. The name Blackpatch is itself quietly arresting, the kind of place-name that suggests old land use or landscape memory without giving anything away.

Beyond its classification and location, the documentary record for this particular site is thin. What can be said with confidence is that souterrains in the west of Ireland tend to be associated with early Christian settlement, often found close to ringforts, the circular earthen enclosures that served as farmsteads for the farming families of early medieval Connacht. Whether that pattern holds here is not currently known from available sources. Mayo has a long tradition of underground archaeology, shaped by its geology and by the generations of people who worked the land above these passages without necessarily knowing what lay beneath.