Workers cutting a two-metre-wide trench as part of the Tuam main drainage scheme exposed a cobbled surface extending over an area of several hundred square metres, a spread of stonework that had been parched in places, cut into in others, and partially destroyed by a nineteenth-century garden plot behind houses on Vicar Street. It was not the cobbling alone that caught archaeologists' attention, but what lay beneath it, and what the cobbling itself implied about the organisation of space in early medieval Tuam.

Investigations carried out under licence by Higgins in 1992 identified a thick cashel-like wall running beneath and around the cobbled area. A cashel is a dry-stone enclosing wall, typically circular or oval, associated here with an ecclesiastical rather than a domestic or defensive function. By the time the trench was opened, this wall had been reduced almost entirely to a low mound of earth and small stones; only a short segment of its outer facing of large stones had survived, though that facing could be traced in the ground on either side of the excavated area. The wall had been robbed out, meaning its stones were systematically removed and reused elsewhere, at some point in the late medieval or post-medieval period. The cobbled surface, which extended both inside and outside the line of the vanished wall, was laid down after that robbing had already occurred. Higgins interpreted the surviving arc as part of an Early Christian ecclesiastical enclosure, one that appeared to run from the grounds of Tuam Cathedral in the direction of Tuam Mart, suggesting a boundary of considerable scale that once defined sacred or institutional space at the heart of the settlement.

Tuam was one of the most significant ecclesiastical centres in medieval Connacht, and the possibility that a large early enclosure underlies much of the present town gives a different character to its modern streetscape. The cobbled surface, the robbed-out wall, and the arc of facing stones all survive only as fragments, their precise extent uncertain, their original function a matter of careful inference rather than clear record.