Roman-designed pontoon bridges, constructed mostly during wartime for the shock and awe of quick raids, and were a specialty of Julius Caesar's.
In 55 B.C., he built a pontoon bridge that was around 437 yards (400 meters) long to cross the Rhine river, which was traditionally thought by the Germanic tribes to be safely out of reach of Roman power.
Roman leader Caligula is well-known for his brief stint as the emperor of Rome, from 37 AD through 41 AD. Some say that Caligula displayed signs of madness during his reign. According to historical accounts, one of these displays of madness was Caligula’s demand for the construction of a floating bridge across the Bay of Baiae so that he could ride triumphantly across it. Some historians dispute the building of this bridge. With differing accounts of exactly what happened during Caligula’s reign as emperor, we may never know whether the floating bridge of Baiae was actually constructed, but it remains a lasting story of power, madness, and what happens when the two intertwine.