At Derrynacrit in County Longford, a circular enclosure, the kind of earthwork commonly called a ring fort, a type of enclosed farmstead typically dating from the early medieval period, sits on a low rise amid wet, waterlogged pasture. Or rather, it once did, and its outline was faithfully recorded by cartographers. Today, nothing is visible at ground level.

The site appears on the Ordnance Survey Fair Plan and on the 1837 edition of the six-inch Ordnance Survey map, both of which mark it clearly as a circular enclosure and label it simply "Fort". Those early nineteenth-century surveys were conducted with considerable care, and the surveyors had enough to see and measure to commit the feature to the record. Whatever raised earthwork or ditched boundary once defined the site has since been absorbed back into the landscape, levelled over time by agriculture, waterlogging, or simple erosion in the soft midland ground.