It is all that remained after a catastrophic flood carried the rest of the structure away sometime before 1646, leaving this solitary curve of masonry as an accidental monument to the crossing that once stood there.

The site sits close to where, according to Sherlock writing in the period 1909 to 1911, there had been both a ford and an ancient bridge serving the Leixlip crossing. A ford is simply a shallow stretch of river where people and animals could wade across, and it was common for bridges to develop near such points once traffic increased. The Salmon Leap, a natural feature of the Liffey where the river drops and salmon were historically seen jumping upstream, was clearly a significant landmark in the local landscape long before the flood erased most of the bridge. Fitzgerrald, writing in the period 1896 to 1899, included a photograph of the surviving arch in his work, which gives some sense of how the structure appeared in the late nineteenth century, already reduced to this one remnant.

The surviving arch sits within the grounds of Backweston Park, which shapes how accessible it is to the casual visitor. The area around Leixlip retains a good deal of riverside character, and the Salmon Leap itself is a recognised geographical feature along this stretch of the Liffey. Anyone with a particular interest in early infrastructure or in the physical traces of pre-modern river crossings will find the arch quietly compelling precisely because of its incompleteness: the flood damage that destroyed the rest of the bridge has, paradoxically, preserved this section in a kind of suspended ruin. The photograph documented by Fitzgerrald is worth tracking down before a visit, if possible, to understand how the arch would have read within the fuller structure it once formed part of.