A single shaped stone, lying half-sunken in a field in County Kildare, is about as quiet a piece of evidence as history tends to leave behind. Yet this arch-stone, measuring roughly three quarters of a metre long and carefully worked with chamfered and rebated edges, points to the likely existence of a castle that no longer stands above ground. Chamfering refers to the bevelling of a stone's edges at an angle, a technique common in medieval ecclesiastical and defensive architecture; rebating involves cutting a step or recess into the stone so that another element could seat against it. That both techniques appear on this single fragment suggests it once formed part of a dressed opening, perhaps a doorway or window, in a building of some pretension.

The stone was found lying partly earthfast, meaning it had sunk partially into the ground over time, in the field to the north-east of the landmark known as the Chair of Kildare. That feature, a natural or modified rock formation that lends its name to the wider townland of Carrickanearla, appears to have been accompanied at some point by a castle, now completely levelled and otherwise unrecorded above the surface. The arch-stone may be one of the last surviving physical traces of that structure, displaced from its original position and left in the field as the building around it disappeared, whether through deliberate demolition, stone-robbing over generations, or simple decay.