It is a rath, the Irish term for a ringfort, the kind of enclosed farmstead that was built in considerable numbers across Ireland during the early medieval period, roughly between the fifth and twelfth centuries. Most raths consisted of a circular bank and ditch enclosing a domestic space, and this one at Tullig conforms to that basic pattern, though time and agriculture have worn it unevenly. The southern arc of the enclosing bank has been almost entirely levelled, while the northern stretch still rises to around 1.35 metres above the surrounding ground. Where erosion has cut through the bank, the construction method has been exposed: a basal course of large boulders, packed over with earth and gravel.

The interior is where the site becomes quietly complex. A sod-covered hut, oval in plan and just over four metres long, interrupts the southern bank and pushes its outline outward in a slight bulge. Only the lowest courses survive, reaching perhaps forty centimetres in height internally, but the stone walls are legible beneath the turf. A curved section of walling on the western side may indicate a second hut, set against the inner face of the bank. Most intriguing, perhaps, is something no longer visible at all. In 1927 a scholar named Ua Riain recorded what he believed to be a souterrain at the site, one of those narrow underground passages, typically stone-lined, that were dug beneath or beside early medieval settlements and used variously for storage or concealment. No surface trace of it remains today, leaving its presence a matter of record rather than observation, the kind of detail that makes a seemingly modest field monument rather harder to read than it first appears.