It is the kind of thing easy to walk past without understanding what you are looking at, partly because the motte itself commands attention, and partly because the outwork is the surviving fragment of a much larger defensive system that has otherwise vanished.

The motte occupies elevated ground at the confluence of the Dinin River, also known as the Deen, and a southern tributary, a naturally strong position on the eastern edge of Castlecomer town. A castle stood on the motte for centuries, and in 1641 what local historians Carrigan and Orpen both refer to as the Garrison was besieged by Confederate forces for over three months. By the early twentieth century, Carrigan noted that the castle had been entirely demolished, though he observed a small fragment of what he thought might be a barrack still visible on the site. Subsequent scholarship has suggested that the garrison in question was in fact a bastioned fort situated in the north-east quarter of Castlecomer town, and that the pentagonal structure on the motte is an outwork of that fort, built in the late sixteenth or early seventeenth century. An outwork in this context is a detached defensive element positioned outside the main fortification, extending its field of control. The stone walls here measure between 0.55 and 0.6 metres thick, and traces of internal plaster survive on some surfaces, suggesting the structure was once more than a bare defensive shell.