Look at the southern side and you see seven pointed arches of roughly cut limestone blocks, a medieval form that suggests considerable age. Turn to the north side and the picture changes: seven round arches with cut voussoirs and projecting keystones, the product of later reconstruction. The bridge is wearing two eras at once, and most people crossing it would never notice.

The Civil Survey of 1654 to 1656 records a stone bridge over the River Suir at Thurles, described simply as a stone bridge upon the river Shewer, and Barry's Bridge may well be that same structure, retaining at least some of its original fabric beneath later additions. A sketch made by Francis Grose in 1793 shows the bridge with two refuges, small recessed alcoves projecting from the parapet on the upstream, northern side, which allowed pedestrians to step clear of passing traffic. These are gone now, most likely lost when the bridge was widened or rebuilt in the early nineteenth century. That reconstruction seems to have been applied almost entirely to the north face, while the south face was left largely alone, preserving its pointed arches as an accidental record of the earlier structure. Cutwaters, the wedge-shaped projections between the arches at water level, survive on six of the piers; their function is to divide the current and reduce the pressure on the bridge's foundations, a feature common to medieval and early modern bridge design throughout Ireland.