This rectangular enclosure, measuring 90 metres from north-northwest to south-southeast and 40 metres from west-southwest to east-northeast, is surrounded by a substantial fosse, or defensive ditch, that’s approximately 9 metres wide. The site’s designers clearly prioritised security; the southern half features additional protection in the form of earthen banks flanking both sides of the fosse, whilst traces of another bank appear to have once divided the interior space in two.

The main entrance to the site can be found on the southwestern side, positioned near the western corner, suggesting careful consideration of access and defence. Water management also played a role in the site’s design, with a leat, or artificial watercourse, visible at the southern corner. Archaeological surveys have identified what may be a second leat near the northern corner, though this feature requires further investigation to confirm its purpose.

These moated sites, which date primarily from the Anglo-Norman period in Ireland (late 12th to 14th centuries), served as fortified homesteads for colonising families and local landowners. The combination of water-filled ditches, earthen banks, and controlled access points created formidable defensive structures that were relatively simple to construct using local labour and materials. Today, whilst the banks have eroded and the moats have long since dried up, the earthworks at Ballyryan remain clearly visible in the landscape, preserving the footprint of medieval life in County Carlow.