At Oldcastle in County Galway, a small enclosure once existed close to the north-west angle of a medieval bailey, measuring just twelve feet by twelve feet, alongside what appeared to be the ring of a tower or small circular building. No visible trace of either feature survives at the surface today. The site is, in a practical sense, invisible, and yet it remains on record as something that was once there, noticed, noted, and then lost.

The observation comes from the historian Goddard Henry Orpen, who recorded the details in 1916. Orpen was writing in the context of a motte and bailey, the type of fortification introduced to Ireland by the Anglo-Normans from the late twelfth century onward. A motte and bailey consists of a raised earthen mound, the motte, topped with a timber or stone tower, connected to an enclosed courtyard at ground level, the bailey, typically surrounded by a bank and ditch. Within that bailey at Oldcastle, Orpen identified the faint ring of what may have been a tower base and, close by, the outline of a small rectangular enclosure. The dimensions he recorded, roughly three and a half metres square, suggest a modest ancillary structure of some kind, though its precise function was not established. Whether the features were already degraded when he saw them, or whether later land use erased what remained, is not recorded.