The walls were not found through targeted excavation but through a slit trench, the kind of narrow slot cut to allow cables to tie into a main ESB line. It is an almost comically mundane circumstance in which to encounter what appears to be a structure contemporary with one of the earliest planted towns in Irish history.

Fort Protector was established in the 1540s as part of the Tudor colonisation of the Irish midlands, and the town that grew around it, originally called Maryborough, became the county town of the newly formed Queen's County in 1556. When archaeologist Colm Flynn monitored the ground disturbance works for the Portlaoise and Fort Protector Enhancement Project Phase II in 2018, the first slit trench, located just to the northwest of the fort's corner tower, revealed two limestone rubble walls bonded with lime mortar, surviving to two courses in height. Wall 1 runs roughly north to south, is 0.45 metres wide, and appears to continue beneath the existing roadway. Wall 2 runs east to west and sits approximately 3.6 metres from the northern wall of Fort Protector, parallel to it. Together, the two walls form a corner of what would have been a larger building, its floor and northern extent still unexcavated and unknown. Beneath both walls lay a grey gravel-rich deposit, interpreted as a foundation bedding layer, with what may be the original natural subsoil below that. A ditch was also identified in section at the same location, extending from the southern edge of Wall 2 all the way to Fort Protector's outer wall. It appears to have been an external defensive ditch associated with the fort, oriented east to west and likely cut in the same century as the building itself.

The building and ditch are not visible at street level and were preserved in place rather than fully excavated, so there is nothing to see as such. But the knowledge that a 16th-century structure and its associated ditch survive largely intact beneath an ordinary Portlaoise street, at a depth of only 0.2 metres below the road surface, gives the immediate surroundings of the fort's corner tower a different quality on foot.