That quiet administrative oddity is the first clue that something unusual has happened to the landscape around this semi-circular enclosure at Corbrack, on the banks of the Tang River.

The explanation lies in the river itself. At some point in recent history, the course of the Tang River was artificially straightened, a common enough intervention in Irish lowland drainage schemes, where channels were realigned to improve land drainage and reduce flooding. That engineering decision shifted the river's line just enough to move the monument from one county to the other. Originally, the enclosure sat on the south bank of the Tang, with the river curving round to form the natural enclosing element on its north-east side. This is a characteristic arrangement for a cliff-edge fort, a type of enclosure where a natural feature, most often a riverbank, cliff face, or steep slope, is used in place of an earthen rampart on one or more sides, reducing the construction effort required while still achieving a defensible perimeter. The old course of the Tang, now bypassed and silted into stillness, is still legible from aerial photography, tracing the original relationship between the fort and the water that partly defined it.

On the ground today, no surface remains are visible. The earthwork has been levelled, and the site gives nothing away to a casual eye. From aerial imagery, however, a faint arc of trees on the south side of the monument preserves the ghost of the semi-circular enclosure, their roots following a line the landscape itself has otherwise forgotten.