What was once a triple-arched hump-backed masonry bridge now amounts to a single partial central arch, a stub of the north-east arch, and the rubble footprint of the south-east arch. The overall visible remains stretch to just 7.7 metres in length and 4.3 metres in width. What makes the surviving fabric so interesting is the detail still legible in it: the central segmental arch is formed of narrow voussoirs, the wedge-shaped stones that lock an arch together, set on edge rather than flat, and the keystone was apparently cut slightly too large to sit perfectly. Two triangular cutwaters, projecting half a metre upstream at 45 degrees, once divided the river's flow around the piers. On the north side of the south-east arch, the faint imprint of wicker centering, the temporary timber and wickerwork framework over which the arch stones were laid during construction, is still visible in the masonry.

The bridge takes its name from King John, and that connection is more than ceremonial. Esker, in the Liffey valley west of Dublin, was part of a demesne that Henry II had annexed to the crown, and it was organised as a royal manor under John. The bridge is clearly marked on John Rocque's 1760 survey map of County Dublin, and O'Keeffe and Simington, writing in 1991, confirmed the identification. The road it carried likely served St Finnian's medieval church ruins and graveyard, which lie around 100 metres to the north-east. By the time the Ordnance Survey published its six-inch map in 1837, the road had been re-aligned and a new bridge constructed downstream. The mechanism of that change was recorded by D'Alton in 1838: an act of 1771 allowed a Mr Vesey to close the old road running west of the Griffeen through his estate, in exchange for routing a new, shorter road across his land at no cost to the county. The old bridge was simply bypassed and left to the river. Test excavations carried out in 2003 to the west of the bridge uncovered a cut-limestone wall, aligned north-west to south-east and following the river course, which post-dates the bridge itself.

The bridge sits in Esker South, west County Dublin, close to Lucan. The Griffeen River is a small watercourse and the remains are low-lying, so water levels and vegetation will affect how much is visible; visiting in late winter or early spring, before growth thickens along the banks, gives the clearest view of the stonework. The ruined church and graveyard of St Finnian, a short distance to the north-east, form a natural complement to the visit, and together the two sites outline the faint trace of a road that has not been travelled in over two and a half centuries.