To secure their new territory, they constructed an earth and timber motte castle on the south side of what is now Castletowndelvin. This Anglo-Norman fortification may have been built atop an even older Gaelic stronghold called Telach Caíl, though the dense overgrowth of bushes and briars that now covers the monument makes detailed archaeological examination impossible.

The motte rises steeply from its base, crowned by a relatively wide, flat summit approximately 15 metres in diameter that once commanded sweeping views across the surrounding Westmeath countryside. Remnants of a drystone wall revetment can still be glimpsed along the western and northern edges of the base, though much of the original defensive structure has been lost to time and development. The monument now stands rather incongruously within a concrete delivery yard of a hardware store, which wraps around its northern perimeter, whilst a cottage and yard occupy the southwestern base.

Just 65 metres to the west-northwest, a later stone castle replaced the original timber fortification, whilst St. Mary’s church and its associated graveyard lie 70 metres to the west-southwest; together, these monuments form a remarkable cluster of medieval heritage in the heart of modern Castletowndelvin. Despite its current state, surrounded by commercial buildings and residential structures that have obliterated any trace of the original defensive fosse, this overgrown mound remains a tangible link to the Norman conquest of Ireland and the complex layers of Gaelic and Anglo-Norman history that shaped this region.