These structures, typically constructed from drystone walling and roofed with large capstones, were dug into the earth beside or beneath settlement sites. Their precise function is still debated among archaeologists, with theories ranging from cold storage for dairy produce to refuges in times of raid or conflict, and in many cases they were likely both, depending on the moment.

The Ballykill example is recorded as a monument, placing it within a broader landscape of early medieval activity in the west of Ireland, a region where souterrains are known to cluster around the remains of ringforts and other enclosed farmsteads. Mayo has no shortage of such sites, and the presence of a souterrain typically signals that a more substantial settlement once stood nearby, even when that settlement has long since vanished from the surface. Without further detail currently available, the particulars of this structure, its dimensions, the number of chambers, its state of preservation, remain unconfirmed.