The site’s significance dates back to 1161, when the Annals record that Roderic O’Conor, the last High King of Ireland, constructed a ‘Castrum Mirificum’ or ‘wonderful castle’ here. By 1574, the castle had passed into the hands of the Archbishop, reflecting Tuam’s growing ecclesiastical importance during the medieval period.

Historical accounts paint a picture of a once-imposing structure that gradually disappeared into the fabric of the growing town. Writing in 1666, chroniclers noted that castle walls were still standing, whilst Ordnance Survey letters from the 19th century reveal that parts of the bawn wall had been incorporated into the front walls of two public houses. The castle reportedly stood across the centre of Shop Street, just yards from where the Mitre Hotel would later stand. Despite Lewis’s 1873 claim of being able to describe the original castle in elaborate detail, he admitted that only slight remains survived even then.

Today, all that remains visible is a curious D-shaped stone structure embedded in the boundary wall of a supermarket car park, some 230 metres west of Shop Street. This enigmatic feature, measuring roughly 2 metres north to south internally, opens to the north and bears a striking resemblance to a late medieval wall turret. Archaeological excavations in 1979 and further investigations during demolition work in 1987 revealed that the structure extends at least 4.5 metres in height, with a curving outer wall face approximately 3 metres in diameter. Though its exact date and original function remain uncertain, this lone survivor now houses a replica of the famous ‘Chair of Tuam’, serving as a tangible link to the town’s rich medieval past.