Behind the Georgian facades that line this side of the town square, fragments of a 17th-century fortified house and its protective bawn still survive, tucked away in the buildings that replaced them. Sir Francis Rushe, whose father-in-law Sir Henry Duke had been granted the lands of the former Clones monastery, likely constructed this defensive complex shortly after 1603. The castle and its bawn, complete with a ‘great door’ opening onto Castle Street, first appear in documentary records in 1636 and would soon witness one of the darker episodes of the 1641 rebellion when local Protestants sought shelter within its walls; some were murdered whilst the survivors fled to Enniskillen.

A 1741 drawing shows the castle still standing on the western side of a rectangular courtyard, though this represented only part of the original bawn. The gateway pierced the western wall, with what appears to be the northwest corner tower topped with a conical cap visible further north, whilst various gabled structures around the courtyard likely housed the brewhouse, stables and other service buildings mentioned in period documents. The complex’s days were numbered, however; by 1766 a new road to Monaghan had carved through the northern section of the castle garden, and the following year five new houses called the Castle Tenement replaced the castle itself, their construction date of 1767 still visible on a datestone.

Today, thanks to local researcher George Knight’s detective work in 2016, visitors can still trace parts of the original fortress in the buildings behind the Diamond’s eastern side. The most substantial remains include a vaulted chamber on the bawn’s southern side, measuring about 10 metres east to west and originally equipped with narrow musket loops in its walls. Above this vault, the first floor preserves three more defensive loops and a later fireplace inserted into the south wall. The bawn wall itself extends eastward from this structure to the southeast corner before turning north for about 13 metres, punctuated by multiple slit openings that once allowed defenders to cover the approaches; four of these narrow apertures survive in two rows along the eastern wall, their slim exterior openings widening internally to give musketeers room to manoeuvre their weapons.