This medieval earthwork, officially recorded as National Monument No. 603, consists of a substantial mound that rises between 4.5 and 5 metres high. The motte’s base spans nearly 24 metres across, tapering to a summit diameter of about 9.5 metres. Over the centuries, the top has been deliberately flattened and the northeastern to southeastern sides have been cut back roughly a metre above the base, creating a slight platform that likely served defensive or residential purposes.

Recent aerial imagery has revealed intriguing features that weren’t visible from ground level. In 2018, Google Earth captured cropmarks showing what appears to be a bailey; a fortified enclosure that would have accompanied the motte. The cropmark traces the outline of a defensive ditch, approximately 1.5 metres wide, forming a rough semicircle to the south, southwest and west of the main mound. This fosse extends about 75 metres westward, 85 metres to the southwest, and 57 metres south of the motte, suggesting a substantial fortified area once surrounded this Norman stronghold.

The site represents a classic example of motte and bailey construction, the preferred fortification method of the Anglo-Normans who arrived in Ireland during the 12th century. These earthwork castles could be erected relatively quickly using local labour and materials, making them ideal for securing newly conquered territories. The modifications to Rathvilly Moat’s summit and sides suggest it saw continued use and adaptation over time, possibly supporting timber structures or later stone buildings that have since vanished, leaving only the earthen bones of this medieval fortress visible today.