The defensive circuit is only partially legible from the ground: two raised banks with a fosse, or ditch, running between them arc around from the east, through the south, and on to the northwest, before simply stopping. The rest of the perimeter has been absorbed by centuries of grazing and tillage, leaving the western portion as a kind of unfinished thought in the landscape.

The site is a rath, the most common type of enclosed farmstead in early medieval Ireland, typically dating from roughly the sixth to the twelfth century. A rath was essentially a circular enclosure defined by one or more earthen banks and ditches, used to protect a household, its animals, and its agricultural stores. This example at Carrowmore is classed as a bivallate rath, meaning it carried two concentric banks, which generally indicates a site of some status; single-bank enclosures are far more numerous. The surviving circuit measures approximately 51 metres east to west and 48 metres north to south, making it a fairly substantial example. A gap roughly two and a half metres wide on the western side may represent the original entrance, which in raths of this kind was often oriented to face the road or the most frequently travelled approach.