That combination, a place of worship and a crenellated watchtower built into the fabric of a river crossing, is unusual enough to prompt a second look at what was, on the surface, simply a way of getting from one bank to the other.

The bridge is documented as St Bennet or Benedict's Bridge from at least 1384, when King Richard II confirmed the status of one John Horley as parson of the free chapel of Benetbrygge, a chapel on the bridge itself dedicated to the Blessed Virgin. Nine years later, in 1393, the Patent Rolls record a royal licence granted to John Midelton, warden of the chapel of St Mary by Benetysbrigge, to complete and crenellate a stone tower he had begun to build within the bridge adjoining the chapel. The stated reason is unexpectedly direct: robberies, homicides, and other evils committed by Irish enemies and English rebels. Midelton was also permitted to construct any other fortifications he judged necessary, provided free passage over the bridge was maintained for all lawful travellers. The chapel appears again in records from 1393 and 1419, suggesting it remained in use for at least a generation after the tower went up. By 1640 the property is listed under a Sir Edward Blanchvill, as recorded in a terrier accompanying the Down Survey parish map of Killerney.

The medieval structure that once carried a chapel and a crenellated tower no longer stands. By 1743 it had already been replaced, and an anonymous traveller passing through that year noted, a few yards below the present bridge, the ruins of an old bridge which had a small castle at the end of it to defend the passage. That observation places the original crossing a short distance downstream to the south of the bridge that stands today, close enough that the two structures, the one living and the one long since dissolved into the riverbank, would have been visible simultaneously from the same vantage point.