Can a marching army collapse a bridge?
A column of soldiers will never march across a bridge for this
reason. The steady oscillation that occurs can, over time cause
structural issues with even a well built bridge. It may not
actually collapse (although not out of the question) but it can
cause serious damage if the marching approaches the resonant
frequency.
The classic example of resonant frequency that every engineer
has had to watch the video of is the Tacoma narrows bridge. There
are also many examples that Tesla explained on this subject.