This Norman fortification likely dates to the late 12th century, when the manor was held by William de Caunteton, nephew of the Anglo-Norman knight Raymond le Gros. The strategic location had already proven its worth when Diarmuid Mac Murchada landed here in 1167, returning from Wales with plans that would soon bring the Anglo-Normans to Irish shores. The site may have served as a port for the nearby monastery town of Ferns, making it a valuable coastal stronghold.

The motte itself is an impressive earthwork, standing nearly six metres high with a flat top measuring thirteen metres across. A defensive ditch, or fosse, surrounds the mound, though centuries of coastal erosion have taken their toll on the eastern side where the sea steadily claims the earthwork. To the south lies what archaeologists believe to be a bailey; a fortified courtyard that would have contained buildings for the garrison and daily life of the manor. This area, now covered in grass, is naturally defended by the sea to the east and a four-metre-deep gorge to the south, with remnants of an earthen bank still visible along its western edge.

The Caunteton family maintained control of Glascarrig for over a century, developing it into a substantial settlement with forty-eight recorded burgages by 1311. That same year marked the end of Norman occupation when local Irish forces under MacMurchada destroyed the manor, after which the site appears to have been abandoned. Today, the motte stands as a reminder of the complex period following the Anglo-Norman invasion, when new fortifications reshaped the Irish landscape and coastal sites like Glascarrig became contested ground between competing powers.