What survives is a pointed, segmental arch with a cut-water on the upstream side, the cut-water being a projecting wedge of masonry designed to split the current and reduce pressure on the structure. It is modest, almost easy to dismiss, yet the 1837 Ordnance Survey six-inch map still thought it worth annotating as "Piers of Old Br." and "Arch", and the 18th-century mill-race immediately to its north continued the same line of road that once crossed it.

The bridge at Lucan appears in the documentary record as far back as 1456, when the Statute Rolls under 34 Henry VI prescribed that towers with gates be constructed at two Liffey crossings, one at Kilmainham and one at Lucan, specifically to prevent incursions by "Irish enemies and English rebels" into Fingal by night. The crossing was, in other words, a frontier structure as much as a practical one. The 1654 to 1656 Civil Survey of Dublin described Lucan as having "a verry faire house a Chappell some thatch houses and Cabbins and a good Stone bridge crossing the river Liffey", and the Down Survey maps of the 1650s, compiled under William Petty, show it as a multi-arched humpbacked structure crossing the river adjacent to Lucan House. Rocque's 1760 Map of County Dublin recorded it still standing. The bridge sat at the confluence of the Liffey and the River Griffeen, close to Lucan House and the medieval parish church on the southern bank, and was one of three bridges in the area identified in the archaeological record. By the analysis of Bradley and King in their 1988 Urban Survey of Dublin, the layout of Bridge Street suggests the bridge was a later insertion into the medieval town plan rather than part of its founding logic.

The remains are within the grounds of a house formerly known as Bleach Green and now called Treeslips, near Coldblow on the northern bank of the Liffey outside Lucan. Access is on private land, so the arch is not openly walkable, but its position and the mill-race to its north can be understood in relation to the river. The 1977 inspection by Henry A. Wheeler of the National Monuments Service noted that the one surviving arch belongs to the northern end of the medieval bridge, suggesting the full structure extended further south across the water. Those looking to contextualise the site cartographically can consult the Down Survey parish maps held by the National Library of Ireland, which give the clearest pre-demolition impression of what the full crossing once looked like.