Beneath a triangular patch of ground between Athy Road, Barrack Road, and Carlow Gate Street in Castledermot, Co. Kildare, lies most of a medieval town wall that almost nobody walking past would suspect was there. Only two short stretches of it remain visible above ground, both built in roughly coursed limestone, and together they amount to less than 25 metres of what was originally a circuit of approximately 1,460 metres. The wall once enclosed a pear-shaped area roughly 550 metres by 375 metres, pierced by three named gates, the Dublin Gate to the north, the Friary Gate to the south, and the Carlow Gate to the west. None of the gates survive. The course of the eastern wall remains uncertain, though it was likely defined by the River Lerr.

The two surviving above-ground sections tell part of the story. One sits within convent grounds near the friary, running 13.5 metres long and standing 2.5 metres high. The other, just to its north, is 11 metres long and 3 metres high, and at the point where it meets the site of the Carlow Gate it still shows a wide basal batter, a deliberate outward slope at the base of a wall designed to increase stability and deflect attack, along with two bar holes where a gate beam would once have been secured. The rest of the circuit is underground. In late 1998, an archaeological evaluation by Gearóid Conroy, carried out ahead of a proposed housing development on the site, uncovered the wall's buried remains in some detail. Test trenches revealed a 5.2-metre-wide band of uncut stone and mortar on the western side of the site, and on the eastern side three parallel bands of stony material with a combined width of nearly 13 metres, suggesting the wall may have had a more complex structure in that area than a simple single line. Inside the wall line, the trenches produced medieval pottery sherds and possible ditch features; one drain running toward the wall yielded an iron arrowhead. Outside the wall, a layer of sandy silt contained a medieval pottery sherd and a bronze ring-brooch. A curving band of burnt material in the north-western area of the site may point to activity even earlier than the medieval town itself.