Each of the spans is an impressive 75ft across, and the spandrels are of the 'parallel wall' type, incorporating closed-in voids to lessen their weight. This helped in allowing the engineer to whittle away the thickness of the arch walls and thus save money on materials.

It is the first bridge to have been built using this structural technique and, says a commentator, if the hollow spandrels were "not the most daring of [Smeaton's] innovations in bridge construction, they were certainly the most successful".

As on all his major bridges, Smeaton decorated the spandrels with central masonry circles, each with four keystones and moulded rims. The original black rubble masonry with which these decorations were picked out remain intact at both Perth and Coldstream.

Resident engineer: John Gwyn