Lios Tuathail, meaning Tuathal's or Toole's Fort, refers to a rath, a type of enclosed farmstead typical of early medieval Ireland, usually consisting of a circular area ringed by one or more earthen banks. This particular example is what archaeologists call univallate, meaning it has a single enclosing bank rather than the multiple concentric rings found at more elaborate sites. The fort gave its name to the settlement that grew up around it, and the settlement eventually grew large enough to absorb the fort almost entirely.

The rath sits behind Gurtinard House, and what survives of it tells a story of gradual absorption into the working landscape. The earthen bank is intact only along the northern arc running through east to the south-east, and at some point that surviving stretch was incorporated into an ordinary field boundary, with its outer face later reinforced in stone. The rest of the circuit has faded to little more than a vague undulation in the ground. Where the bank does survive, it still has some presence: rising to between one and 1.6 metres on the exterior and around a metre on the interior, and spreading to seven metres at the base. Inside the south-western portion of the enclosure there is a circular mound measuring 8.3 metres across and 1.4 metres high, the purpose of which is not recorded but which adds another layer of quiet complexity to the site. The name Listowel has been marked on all editions of the Ordnance Survey's historic maps, a small but consistent acknowledgement that the town and the earthwork behind it were never entirely separate things.