That arc is the western half of an early medieval ringfort, a type of enclosed farmstead built in Ireland roughly between the fifth and twelfth centuries, where a family and their livestock would have lived within a circular bank for both status and security. The eastern half has been lost, but what remains at Callatrim is substantial enough to read clearly in the landscape.

The surviving bank stands 2.2 metres high and is earthen in construction but faced with stone, a combination that suggests some care and investment on the part of whoever commissioned it. The enclosure would have measured around 33 metres in diameter when complete. Just outside the bank, a fosse, essentially a defensive ditch, runs parallel to it, though it is shallow now at only 0.2 metres deep, worn down by centuries of grazing pasture. Where the eastern portion of the bank and fosse have been levelled at ground level, their outlines remain legible from the air, showing up as cropmarks or soil discolourations of the kind recorded through aerial survey programmes.

The site sits in working pasture, and the western arc of the original enclosure has effectively been absorbed into the field boundary system, which is how a great many Irish ringforts survive, their geometry quietly preserved by farmers who continued to use the banks as convenient divisions long after their original purpose was forgotten.