Originally built as a church in the 12th or 13th century, this structure underwent a remarkable conversion in the late 15th or 16th century when a pointed stone vault was inserted, effectively transforming the building into a residential tower. The surviving portion, possibly the original chancel, measures about 14 metres east to west and stands on gently sloping ground, with a round tower visible just 25 metres to the southwest. The building’s roughly coursed rubble masonry walls retain much of their original fabric up to the first floor level, though the structure has seen various repairs over the centuries, including significant conservation work in the 1930s when ivy was removed and tie bars were inserted to stabilise the vault.

The architectural details reveal the building’s dual purpose as both sacred and secular space. The ground floor retains traces of its ecclesiastical origins, including what appears to be an original chancel arch position, now occupied by a pointed doorway flanked by rectangular openings with glazing bar holes. The residential conversion is most evident in the upper floors, accessed via a mural staircase built into the north wall. The second floor chamber served as comfortable living quarters, complete with five windows including two elegant two light ogee headed examples with carved details in their spandrels. A fireplace with a stepped chimney provided warmth, whilst wall cupboards offered storage. The remains of what was likely a garderobe, supported on corbels projecting from the north wall, speaks to the domestic comforts expected by its late medieval inhabitants.

Historical records indicate that by 1563, Aghaviller formed part of the manor of Knocktopher and was granted by Thomas, Earl of Ormond to Oliver Grace, placing it firmly within the sphere of Anglo Norman influence in the region. Evidence of an adjoining building to the west, with its steep roof line still visible in the masonry, suggests this was once part of a larger complex. The structure stands today as a National Monument, offering visitors a chance to explore how medieval Irish churches were sometimes repurposed as fortified residences during the turbulent late medieval period, when security concerns often trumped purely religious considerations.