No earthwork rises above the pasture, no bank catches the light at dusk, no hollow hints at a former enclosure. The site is, by every practical measure, invisible, and yet it is there, or was there, recorded on paper when the ground still held some trace of it.

A ringfort, sometimes called a rath, is a circular enclosure defined by an earthen bank and ditch, typically dating from the early medieval period and used as a farmstead or place of refuge. The Tully example survives in the documentary record rather than the landscape. It appears on an estate map drawn in 1821 by a surveyor named Alexander Wallace, where it is marked as a circular enclosure and labelled simply 'Fort'. The map, held in the National Archives of Ireland as MS 1451 under the title 'Map of the lands of Tully, Co. Longford', places the feature on the eastern slope of a low rise in what is now pastureland. At some point between that survey and the production of the Ordnance Survey six-inch maps, the site either vanished from notice or was levelled entirely; it does not appear on any edition of those maps. Whether through agricultural clearance or gradual erosion, the physical form was lost while Wallace's careful draughtsmanship preserved its outline.

What the 1821 map offers, then, is a small window onto a landscape that no longer exists in three dimensions. The ringfort at Tully joins a long and quietly melancholy category of Irish monuments known only because some estate agent or surveyor happened to record them before the land was turned over completely to farming.