This earthwork fortress, likely dating from the Norman period, consists of a circular ringwork measuring approximately 29 metres north to south and 28.6 metres east to west. The main defensive structure comprises an impressive earthen bank, standing about one metre high on the interior and over two metres on the exterior, with a base width of 5.1 metres. Beyond this lies a wide, flat-bottomed fosse that remains waterlogged to this day, measuring 2.1 metres across and plunging to a depth of nearly 2.4 metres.

The original entrance to the ringwork can be found in the east-northeast quadrant, where a 3.7-metre-wide causeway crosses the defensive ditch. Stone protrusions visible in both the causeway and outer bank hint at more substantial construction elements, possibly the remains of a gate structure or bridge supports. A second, smaller causeway was added later in the north-northeast section, though curiously, there’s no corresponding break in the inner bank to allow access. The interior of the ringwork has developed a slightly dished profile over the centuries and is now overgrown with trees, brambles, and scrub.

What makes Ballyherberry particularly interesting is its attached bailey, which extends along the eastern and southern sides of the ringwork. The eastern section of this outer ward is defended by another earthen bank and U-shaped fosse, whilst the western boundary follows an existing field division. The bailey stretches some 37 metres from the ringwork’s outer bank on its southern side, creating a substantial additional defended area that would have housed auxiliary buildings, stables, workshops, and storage facilities essential to the castle’s daily operations. Together, the ringwork and bailey represent a complete Norman fortification system, demonstrating the military engineering techniques employed during the medieval conquest and settlement of Ireland.