The castle first appears in historical records as the residence of John boy O Munehane (also known as Monaghan) in 1582, marking it as an important seat of local power during the late Tudor period. By 1650, the political landscape had shifted dramatically; William Monaghan of Fortel found himself among those transplanted to Connaught during Cromwell’s reorganisation of Irish land ownership. The Down Survey barony map of Ballybritt, compiled during this turbulent period, marks the tower at ‘Fortalla, Shanvagh and Bealnahuoly’, whilst later Ordnance Survey maps from the 19th century identify it simply as ‘Fortel Castle’.

Today, visitors to Fortel encounter a structure that tells multiple stories through its architecture. The surviving west and southern walls of the L-plan house rise four storeys high, though much of what meets the eye dates from 18th-century renovations rather than the original medieval construction. These later improvements included the addition of brick fireplaces and wooden floors, transforming what was once a defensive structure into a more comfortable residence. Archaeological evidence reveals wall footings of a corner tower at the north-east angle, suggesting the castle was once more extensive than its current remains indicate.

The medieval character of Fortel Castle still shines through in several distinctive features. A flat-headed window in the north wall at first-floor level represents the original architectural style, whilst the west wall once boasted a machicolation at wall-walk level, positioned slightly off-centre to the south. This defensive feature likely protected the ground-floor entrance below, allowing defenders to drop projectiles on unwelcome visitors. Based on these surviving elements and historical records, archaeologists date Fortel as a late 16th or early 17th-century fortified house; a structure built during Ireland’s transition from medieval tower houses to more modern fortified residences, then substantially altered during the Georgian period to meet changing tastes and requirements.