floating bridge, used primarily but not invariably for military purposes. A pontoon bridge was constructed in 480 BC by Persian engineers to transport Xerxes' invading army across the Hellespont (Dardanelles). According to Herodotus, the bridge was made of 676 ships stationed in two parallel rows with their keels in the direction of the current. Alexander the Great is said to have crossed the Oxus by rafts made of his soldiers' tents of hide stuffed with straw.
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