A boat-bridge consists of a track laid on a number of boats anchored parallel in the stream, or moored to ropes or chains which pass from bank to bank.
The bridge thrown across the Hellespont by Xerxes when he invaded Greece, 480 B. C., had a length of 500 paces, and was supported on ships used as pontons. Suspension cables of flax and biblos united the ships, transverse beams were laid on the cables; the beams supported plank and earth, and the army marched across, bag and bing fortified towns, sieges, etc.
The Greeks had but small rivers, and had no stone bridges until after the Roman conquest.
We learn from the Greek historians that bridges were constructed by Cyrus (536 B. C.), Darius (490 B. C.), Xerxes (480 B. C.), and Pyrrhus (280 B. C.). Each of these was a military bridge for a special purpose, and had no permanent character.
The bridge of Cyrus, over the Meander, was supported on boats, like those which crossed the Bosphorus and the Hellespont unde
It works in grooves in the dock walls, and acts as a lock-gate.
See Plate XIX. page 884.
（Military Engineering.) A temporary military bridge supported on flat-bottomed boats or floats, termed pontons.
The use of boats or floats for supporting temporary bridges is of great antiquity.
Darius Hytaspes and his army crossed the Bosphorus on a bridge of this kind in order to invade Greece 493 B. C., and his successor Xerxes constructed one across the Hellespont, 480 B. C., for the same purpose, of which we have a description in Herodotus.
Its length was 500 paces.
Ships were used as pontons; suspension-cords of flax and biblos united them; transverse beams were laid on the ropes, planks on the beams, soil on the planks, and the armies crossed thereon.
Cyrus, according to Xenophon, threw over the Meander a bridge supported on seven boats.
Pompey crossed the Euphrates by a boat-bridge during the Mithridatic war.
Portable bridges were designed by the
6. (Shipbuilding.) A spar, hooped at the end, and used for moving timbers on end by a jolting blow.
7. (Nautical.) A projecting device at the bow of a war-vessel, designed to crush in the sides of an adversary by running against her end on.
It formed a very important means of offense in ancient naval warfare, the prows of galleys in former times having been, as may be seen by the examination of old coins and sculptures, generally furnished with rams.
At the battle of Salamis, 480 B. C., Queen Artemisia, an Asiatic Greek herself, though allied with the Persians, effected her escape by running down a Persian ship, causing the Greeks to mistake her galley for one belonging to their own fleet.
The term ram is also applied to a ship provided with such an appendage.
The great ship of Ptolemy Philopator had two heads.
two sterns, and seven beaks, one of which was longer than the others.
With the introduction of armor-plating the use of the ram has been revived in mode