It has been there, in some form, for well over a thousand years, and the cows appear entirely unbothered by this.

This is a rath, the commonest class of monument in the Irish countryside. A rath is a ringfort, a type of enclosed farmstead built predominantly during the early medieval period, roughly between the fifth and twelfth centuries. Farmers of middling status enclosed their homesteads with earthen or stone banks and outer ditches, called fosses, partly for security, partly as a declaration of land ownership and social standing. The Derryvreen example measures around 35 metres in diameter, enclosed by a stone bank with an external fosse roughly 0.4 metres deep. A pathway cuts across the western half of the interior from north to south, suggesting the enclosure has long been folded into the working landscape around it rather than set apart from it. The interior is heavily overgrown, which is itself a kind of preservation: vegetation slows erosion and discourages casual disturbance, even as it obscures whatever traces of occupation might remain beneath the surface.