Built in the late 12th or early 13th century by Theobald Walter, this earth and timber fortification served as the administrative heart of the newly established Anglo-Norman Manor of Thurles. Though no surface traces remain today, the circular outline of this once-formidable structure can still be spotted on the first edition Ordnance Survey maps, and its memory lives on in the name of nearby Moat Lane.

According to historical accounts, this earthen mound originally stood an impressive 30 metres high before its destruction around 1800. The motte castle was strategically positioned inside or adjacent to the bawn of the 15th century Black Castle, also known as Thurles Castle, which still stands about 35 metres to the south. By 1752, the medieval defensive structure had been transformed into a garden feature, described as 'a mount with a winding ascent', suggesting it had been incorporated into the landscaped grounds of Thurles Castle as a decorative element rather than a military one.

The earliest reliable reference to a castle at Thurles appears in a charter granted by Theobald Walter before his death in 1206. By 1338, the manor complex had evolved to include various stone buildings; a chamber, chapel, kitchen with stone walls covered in shingle, and a bakehouse with stone walls and straw covering, though by then these structures were reportedly in poor condition with no one willing to rent them. The site represents a fascinating example of how medieval fortifications evolved over centuries, transitioning from military strongholds to ornamental landscape features before ultimately disappearing entirely beneath modern development.