The one crossing the Gweestin River at Lissavane does that, but then keeps going. Beyond the main span, the structure extends across the floodplain to the southeast with three additional dry arches, meaning arches built not over the river itself but over ground that floods periodically. It is a practical solution to a landscape that refuses to stay dry, and it gives the bridge an elongated, almost episodic quality that sets it apart from a straightforward river crossing.

The bridge runs on a northwest to southeast axis and measures 5.3 metres in width. Its three main arches are segmental in form, the curved shape that became common in road bridge construction as it allowed for a lower, flatter profile than the older semicircular arch. The voussoirs, the wedge-shaped stones that lock an arch together, have been masked over in concrete at some point, which obscures some of the original detail. The main body of the bridge is built of roughly coursed and uncoursed rubble, while the section incorporating the dry arches is constructed from angular random rubble, suggesting the two portions may not have gone up at precisely the same time, or at least drew on different materials. On the downstream side of the piers sit two low pointed cutwaters of rusticated ashlar, the projecting wedge-shaped elements that deflect the river current and reduce pressure on the structure. A low buttress occupies the downstream side between the main bridge body and the outermost dry arch, tying the two sections together.