This paper establishes relations—historical, material and evidential connections—between two responses to a ‘crisis’. The first features in the history of industrialised iron construction, specifically period reporting on the spectacular collapse of the River Dee bridge in Cheshire, England, in 1847. The second response highlights a blind spot in the historiography of modern architecture. Robert Stephenson became suspect when his cast- and wrought-iron railway bridge across the River Dee failed, resulting in death and injury and continuing uncertainty as to its cause. At the time the incident sparked national furore, setting off a coroner’s inquest followed by a Royal Commission into the perilous state of Britain’s bridges. The inquest jury concluded no one was to blame; rather, it was an accident brought about by use of iron, an uncertain and “treacherous” metal. This explanation has failed to satisfy contemporary materials specialists who have reopened the case, albeit under different terms of reference.      The paper examines the initial verdict, firstly, in view of aspects of the social context of evidence and proof prevailing at the inquest and, secondly, given historical writing on iron construction whereby the inquest’s seemingly imprecise and arbitrary judgment is taken as sign of the subsequent progress of engineering as a practical and moral science. This paper adopts the leitmotif of ‘crisis’ to highlight a parallel history that challenges progressivist narratives of industrialised iron construction and modernist architecture. It invites reflection on the provenance and unstable forms of agency associated with engineering as a propositional and socially contingent enterprise.