This is a rath, the most common type of early medieval settlement monument in Ireland, essentially a raised enclosure formed by a circular earthen bank and an outer ditch, or fosse, which would once have enclosed a farmstead or the dwelling of a local landowner of modest standing.

The Derrycashel example measures roughly 26.5 metres east to west and 26.3 metres north to south, making it a compact but well-defined example of the type. Its enclosing bank ranges from about 2.7 to 4 metres wide, and while the internal face has been worn down to as little as 10 centimetres in height, the external face still rises to nearly a metre in places. An outer fosse, running north-east to west-south-west, adds a further layer of definition to the enclosure. The original entrance, 2.5 metres wide, opens to the south, which is a common orientation for ringforts across Ireland, possibly for reasons of shelter or social convention. The site has not escaped entirely unaltered. Field banks, the low earthen boundaries used to divide agricultural land in more recent centuries, have clipped the western and northern edges of the perimeter, and a further bank that once crossed the interior from north to south on the eastern side has since been removed, leaving the interior relatively clear.