Why are soldiers not allowed to march in step over bridges?

The rule traces back to an accident in 1831, when 74 soldiers marching in step crossed a suspension bridge in Broughton, England, causing resonance vibrations that destroyed it. Since then, many countries, including Germany, require troops to break step when crossing bridges. The reason is pure physics: regular steps can set a bridge into dangerous oscillations that amplify with each stride. Although closed marching formations rarely cross bridges today, this old caution lives on in modern construction and testing standards for footbridges.