But locked inside that concrete and tarmac structure is a late medieval bridge that has been carrying travellers into Connacht for at least four and a half centuries, its original stonework quietly sandwiched between later extensions on either side.

The name Ballinasloe derives in part from the ancient ford that once crossed the Suck here, and a castle on the eastern bank reinforced the strategic importance of the crossing long before any bridge existed. The first documentary mention of a bridge at this point dates to 1579, when a government record noted that one had been "lately made at Ballinasloe over the river of Suck at our own charges," with the explicit purpose of keeping the nearby castle in crown hands as "the common passage into Galloway." The original structure appears to have been built in two separate sections. The eastern section, standing close to the castle, originally comprised at least four spans and measured 4.25 metres in width; three of those spans still survive, now pressed between a downriver extension dating from 1745 and a modern concrete addition on the upriver side. The western section retains all four of its arches, with massive cutwaters, probably added in the nineteenth century, projecting from the upstream face to deflect the force of the river. The cutwaters serve a practical function: by splitting the current around the piers rather than letting it pile against them, they reduce the erosive pressure that would otherwise undermine the structure. The arches throughout both sections are of three and four-centred design, a pointed form common in late medieval Irish bridge building, springing from wide piers.

Because the medieval fabric is incorporated into the working road bridge, there is no single vantage point from which the full history of the structure announces itself. The most telling views are from the riverbank, where the varying widths and materials of successive phases become readable, and where the profile of those original arches can still be made out beneath the accumulated centuries of modification.