What you are looking at, if you know to look, is a rath, the Irish term for a ringfort, a type of enclosed farmstead that was the dominant form of rural settlement in early medieval Ireland, roughly from the fifth to the twelfth centuries. Thousands of them survive across the island in varying states of preservation, but each one occupies its landscape with a particular logic, and this example at Lettertinlish is no exception.

The fort sits atop an east-west ridge, now given over to pasture, and measures 26 metres across in both directions, making it a near-perfect circle. It is defined by a low earthen bank that reaches a maximum height of 1.3 metres, modest by the standards of some raths but still legible as a boundary. To the north, the fosse, the defensive ditch that would originally have run outside the bank, has silted up over the centuries. That silting is typical of sites that have been under agricultural use for generations; the ditch slowly fills with runoff, animal disturbance, and the general settling of soil over time, until what was once a clear channel becomes little more than a depression. The ridge-top position would have made practical sense to whoever farmed within this enclosure, offering drainage, visibility, and a degree of natural defensibility.