The experiments of William Fairbairn, and the mathematical analysis of Eaton Hodgkinson had shown by a series of experiments that an enclosed box girder, made of riveted wrought iron, combined relative lightness with great strength. The tubular wrought-iron girder – be the cross-section rectangular, triangular or circular – formed a most efficient truss component. If the cross-section was large enough it could be self-supporting. It was Fairbairn's experiments that led to the design of the Menai and Conwy bridges. Stephenson had originally proposed using a box-girder section suspended from chains. The box section would, he argued, be stiff enough to overcome the conventional problems of the bridge-decks of suspension bridges. In the event, Fairbairn showed that a properly constructed box girder would be strong enough so that the chains could be dispensed with. Nevertheless, the decision (not to use chains) was taken late in the project, so the Britannia bridge support towers were still built with holes for the chains. Stephenson's box-girders were a great innovation, and using steel or pre-stressed concrete instead of wrought iron, box-girder construction is the standard today for large bridges. But as Berridge has observed, "Brunel was never one to follow fashion for fashion's sake... (at Chepstow)... Here was the real engineer at work, designing the bridge to suit the site and the best way of getting it into position".