Xerxes' Pontoon Bridges

Xerxes' Pontoon Bridges were constructed in 480 BC during the second Persian invasion of Greece upon the order of Xerxes I of Persia for the purpose of Xerxes’ army to traverse the Hellespont (the present day Dardanelles) from Asia into Thrace, then also controlled by Persia (in the European part of modern Turkey).

The bridges were described by the ancient Greek historian Herodotus in his Histories, but little other evidence confirms Herodotus' story in this respect. Most modern historians accept the building of the bridges as such, but practically all details related by Herodotus are subject to doubt and discussion.

Herodotus relates in his Histories that the Second Persian invasion of Greece already intended by Darius I was carefully prepared by his son Xerxes I. A canal crossing the Athos peninsula was constructed. Among many other things he also ordered ships of war to be furnished and ropes of papyrus and of white flax to be prepared for the bridges.

During the time Xerxes and his huge army were marching from Sardes to Abydos, then an important harbour on the Hellespont, two bridges were built from there to the opposite side near Sestos over a distance of seven stadia (some 1,300 m or 1,400 yd), but were destroyed by a storm before the army arrived. Xerxes was enraged and had those responsible for building the bridges beheaded. He is then said to have thrown fetters into the strait, given it three hundred whiplashes and branded it with red-hot irons as the soldiers shouted at the water.

New bridges were constructed by lashing penteconters and triremes together. 360 ships were used to construct the northeasterly bridge and 314 ships were used for the southwesterly bridge. Anchors were lowered at either end of the boats to keep them in place and cables, alternatively made of white flax and papyrus, were stretched from shore to shore to hold the boats together and were tightened by large winches. The weight of the cables of flax is said to have been one talent per cubit. Three openings were provided for the passage of small boats. Wooden planks were laid across the cables, and brushwood and soil used to cover the planks and form a dirt roadway. Screens were put up on either side of the bridges to prevent the horses and other animals from panicking at the sight of the sea below.

...
Wikipedia