The north-south road running west of this earthwork at Tully gives the site a noticeably wide berth, curving around the rath's western and northern sides as though the original road-builders preferred to keep their distance. That kind of quiet avoidance, preserved in the modern landscape, is one of the more telling signs that a site once carried real social or symbolic weight in the local area.

The earthwork itself is a rath, a type of roughly circular enclosure defined by earthen banks and ditches that was the standard form of enclosed farmstead or settlement in early medieval Ireland, in use broadly from around the sixth to the twelfth centuries. At Tully, the enclosure sits on the spine and north-facing slope of a drumlin ridge, one of the rounded glacial hills that give County Monaghan much of its corrugated character. The interior measures roughly forty metres east to west and thirty-six metres north to south, sloping gently downward to the east. Its defining bank is overgrown but substantial, rising about three metres on the exterior at its south-southwest section, with an outer fosse, a defensive ditch, roughly ten and a half metres wide at the top on the south-west side. Beyond that, faint traces of an additional outer bank survive from south-west around to north-north-west. The original entrance, about three metres wide at the base, faced east-north-east but is now closed. South of the main enclosure, a roughly square area of approximately forty-five metres on each side appears to have been deliberately avoided by the road. Researchers have suggested this may represent the footprint of an annexe, a secondary enclosure attached to the main rath, which would have added further space for livestock or other activities associated with the settlement.