This is a rath, a ringfort of the kind that once served as an enclosed farmstead during the early medieval period, typically surrounded by an earthen bank and an outer ditch called a fosse. The example at Derrynagalliagh is roughly 42 metres across, its enclosing bank of earth and stone still surviving to a width of two and a half to three metres in places, though only about 40 centimetres high. That modest profile is part of what makes it easy to overlook.

The site has not come down to us intact. Along its western to east-northeast arc, the original bank has been absorbed into modern field boundaries, its fabric quietly repurposed over generations of agricultural reorganisation. On the southern side, from south-southeast around to south-southwest, it has been levelled entirely. No fosse survives, and no clear evidence of an original entrance remains visible. What is left is essentially a fragment of a perimeter, a low earthwork that has been simultaneously preserved and eroded by the same centuries of farming that shaped the landscape around it. This incremental loss is common among Irish ringforts, thousands of which have been similarly reduced or erased, making even a partially surviving example worth noting.