The arch would consist of iron ribs. Fawcett says, "The reasons for not using wrought iron was due to some engineers' distrust of rivetting, the relatively small size of wrought iron plates then available, and the higher cost… On 1 October 1845 when the Newcastle and Berwick Board instructed T E Harrison for their bridges, none of the uses of wrought iron had been developed far enough to be considered as an alternative to cast iron for the High Level Bridge. A tubular bridge might have been considered by Robert Stephenson but the distance between solid and reasonably shallow foundations would have given a span much larger than the Britannia Bridge."