It is not immediately dramatic, but the more closely you read its shape, the more deliberate it becomes: an oval platform some 47 metres north to south and 30 metres east to west, raised on a steep-sided mound roughly two metres high, ringed by a substantial bank of earth and stone that runs from the southeast around through south and southwest, then curves back around from the north-northeast. Where the ground falls away naturally at the east and west flanks, the ridge itself was simply pressed into service as a ready-made boundary, the builders seeing no need to duplicate what the topography had already provided.

This is a rath, the Irish term for a ringfort, the most common monument type in the Irish landscape. Ringforts were enclosed farmsteads, built and occupied predominantly during the early medieval period, roughly the fifth to twelfth centuries, used to protect a household, its people, and its animals. At Tanrego the design shows characteristic features of the type: a cleared interior platform, a surrounding bank and ditch arrangement, and a probable original entrance on the southwestern side, about three metres wide, positioned where the enclosure would have faced away from the prevailing exposure of the ridge. Within the northern half of the interior there is evidence of a possible hut site, which would have been where the occupants actually lived. The break in the outer bank to the north, between five and six metres wide, may be a later opening rather than the original entrance.

What gives the Tanrego rath a quietly layered quality is how thoroughly it has been absorbed into the later agricultural organisation of the ridge. The disused field banks that run across the surrounding hilltop meet and merge with the terminals of the outer rath bank, meaning that centuries of subsequent farming have grown up around this structure, using it partly as a boundary marker, partly as convenient elevated ground. The monument and its landscape have long since become inseparable.