There is actually little evidence here that a resonance excited by marching soldiers caused this bridge to fall. The article says that, as usual, the soldiers were instructed to break step when crossing. The article cites a powerful thunderstorm, the effect of strong gusts being 'caught' by the massed soldiers on the bridge, and corrosion of the cables at their anchorages, as likely causes. A survivor reported that the soldiers were stumbling around as if drunk, and could barely stand. There was some speculation that the motion of the bridge caused the soldiers to respond in a coordinated way that exacerbated the swaying, but lurching from side to side is hardly marching.
Contrary to what the grandparent post says, few bridges are susceptible to being brought down by marching.
Contrary to what the grandparent post says, few bridges are susceptible to being brought down by marching.