The site measures roughly 27 metres from east to west and 13 metres from north to south, making clever use of the coastal topography that would have made it nearly impossible to approach except from one direction. The western approach, where the land connects to the mainland, still bears the defensive features constructed by its ancient builders: an earthen bank standing about 1.25 metres high and a fosse, or defensive ditch, that stretches approximately 12 metres long and 5 metres wide.

What makes this particular fort interesting is the construction method of its defences. The fosse was carved directly from the bedrock, a labour-intensive process that would have required considerable effort and planning. Archaeological evidence suggests that some of the stone excavated from this rock-cut ditch wasn’t simply discarded; instead, it appears to have been repurposed as facing material for the outer side of the earthen bank, creating a more formidable barrier against potential attackers.

This type of coastal fortification was relatively common in ancient Ireland, where communities took advantage of natural defensive features whilst adding their own modifications where the landscape left them vulnerable. The fort at Carthage represents a typical example of how Iron Age peoples adapted their defensive strategies to the local terrain, creating strongholds that required minimal construction whilst maximising defensive capability. Its survival allows us to understand how our ancestors lived, defended themselves, and shaped the landscape thousands of years ago.