Built into its base is a small, square culvert opening, designed to let water pass through the wall rather than pool against it. It is a practical, unhurried piece of construction, and almost nothing about it announces itself.

The causeway is not a remnant of the late medieval castle whose moat it crosses. That earlier fortification, a bawn castle, predates it considerably; a bawn being an enclosed courtyard or defended enclosure typically associated with tower houses and plantation-era strongholds. The causeway appears instead to belong to a later phase of activity on the same ground, most likely the eighteenth or early nineteenth century. It shares the same drystone construction method as the field wall running to the east, and both seem connected to a now-destroyed dwelling referred to locally as Bawn House, which once stood to the south-west. That house gave the townland its name, and the causeway was almost certainly built to serve it, offering dry passage across what had by then become a waterlogged depression rather than a functioning defensive feature. The moat, no longer needed for any military purpose, had simply been allowed to fill in, and the causeway was the practical solution to what it left behind.