Where pasture now rolls unbroken, there was once a rath, the Irish term for a ringfort, the circular earthen enclosures that served as enclosed farmsteads across early medieval Ireland, typically dating from roughly the sixth to the twelfth century. Nothing of it remains above ground today, but the 1842 Ordnance Survey six-inch map recorded it clearly, rendered in the cartographers' hachured shorthand for a circular earthwork roughly twenty metres in diameter.

By the time anyone thought to formally catalogue it, the site had already been levelled, leaving no visible surface trace. Some quarrying in the area of the enclosure likely hastened or completed its removal. That the OS surveyors caught it at all is something of a small fortune; the 1842 mapping project was the first systematic large-scale survey of the Irish landscape, and it inadvertently became the last witness to hundreds of earthworks that would not survive the following century. The Tinnascart rath is one of many such sites that exist now only as a mark on an old sheet of paper.