Today the remains are low and largely levelled by centuries of agricultural activity, yet historical records and cartographic evidence suggest that the site once formed a clearly defined enclosure of some importance. According to a nineteenth-century entry in Coflein, the site was described in 1870 as a ploughed-down, sub-rectangular enclosure measuring approximately 34 metres across internally. Earlier maps commonly depict the enclosure as a square with rounded corners, measuring around 44 metres from north-west to south-east and approximately 38 metres across, suggesting a deliberately planned defensive structure rather than a natural feature.

Over time, however, the recorded form of Castell Mwrtach has varied significantly in cartographic sources. One of the most intriguing representations appears on a 1964 map, where the site is shown as a distinctly circular enclosure. This change in depiction is highly significant, as circular fortified sites are not characteristic of Norman castles, which typically feature angular layouts, stone keeps, or motte-and-bailey forms. Instead, circular enclosures are strongly associated with early Irish defensive settlements known as ringforts or raths. These structures were widespread in Ireland during the early medieval period and were commonly constructed from earth banks, timber palisades, and occasional stone elements, rather than the masonry castles introduced by the Normans.

The name “Mwrtach” itself provides further evidence of an Irish connection. Linguistic analysis suggests that Mwrtach is the Welsh form of the Irish personal name Murchada. Place-names derived from personal names often indicate ownership or association, and in this case the name strongly implies that the enclosure was linked to an individual of Irish origin. This interpretation aligns closely with the circular form shown on later maps and with the broader historical context of Irish – Welsh interaction during the twelfth century. Prior to the Norman invasion of Ireland, Irish rulers did not build stone castles of the kind seen in Wales; their power centres were instead small, circular fortified homesteads, closely resembling what Castell Mwrtach may once have been.

Additional historical support for this theory appears in nineteenth – century Welsh scholarship. The Chronicles of the Princes (1857) records the name Mwrtach as an alternative form of Murchath, an Irish family name, and refers to Diermait, son of Murcath, who left Wales in 1168 alongside the Norman knight Robert FitzStephen. This Diermait is widely understood to be Diarmait Mac Murchada, the exiled King of Leinster. Having been driven from his throne in 1167 by the High King of Ireland, Diarmait sought military support to reclaim his kingdom. His travels brought him to Wales, where he forged alliances with powerful Norman lords and secured the backing of King Henry II.