What makes this particular rath, or ringfort, worth a second look is its third earthen bank, an additional ring running from the south-south-west around to the north-west, which behaves differently from the others. For most of its arc it follows the line of the outer fosse, the ditch between the banks, but then curves inward to meet the second bank at the north-west. Archaeologists note it may be a later addition, suggesting the site was not necessarily built or used in a single phase.

Ringforts are among the most common field monuments in Ireland, estimated to number around forty thousand across the island, and most date to the early medieval period, roughly the fifth to twelfth centuries. They typically served as enclosed farmsteads for a single family or small settlement, with the banks and ditches providing a degree of protection for people and livestock rather than any serious military defence. This one at Tullig is a bivallate example, meaning it has two concentric banks rather than the single bank more commonly found. The interior measures roughly thirty-one metres across in either direction, making it a reasonably substantial enclosure. The two banks, separated by an intervening fosse, vary in surviving height; the outer bank still stands about 0.9 metres on its exterior face and 1.2 metres to the base of the fosse on its inner side, while the inner bank is more eroded. Both banks have been planted with deciduous trees, which is not unusual for ringforts in farmland, where the earthworks have often survived precisely because the trees discourage ploughing right up to the banks. The entrance, oriented to the east as is common with early medieval enclosures, is slightly wider through the outer bank at 5.6 metres than through the inner at four metres.