nications.

Military bridges are made with trestles, rafts, boats, and other
floating bodies. Rope bridges are also sometimes resorted to by troops
for passing rivers.

_Trestle bridges_ are principally used for crossing small streams not
more than seven or eight feet in depth: they also serve to connect
floating bridges with the shore, in shallow water. The form of the
trestle is much the same as that of an ordinary _carpenter's horse,_
i.e., a horizontal beam supported by four inclined legs. These trestles
are placed in the stream, from twelve to twenty feet apart, and
connected by string-pieces, (or _balks_ as they are termed in technical
language,) which are covered over with plank. The action of the current
against the bridge may be counteracted by anchors and cables, or by
means of boxes or baskets attached to the legs of the trestles, and
filled with stones. A more substantial form may be given to the bridge
by substituting for the trestles, piles, or the ordinary framed supports
so much used in the newer parts of our country.

For examples of the use of bridges of this description we would refer to
Caesar's celebrated bridge across the Rhine; the passage of the Scheldt
in 1588 by the Spaniards; the passage of the Lech in 1631 by Gustavus
Adolphus; the passage of the Danube in 1740 by Marshal Saxe; the great
bridge across the Var during Napoleon's Italian campaigns; the passage
of the Lech in 1800 by Lecourbe; the bridges across the Piava, the
Isonso, &c., in the subsequent operations of the army in Italy; the
celebrated passage of the Danube at the island of Lobau in 1809; the
passage of the Agueda in 1811 by the English; the passages of the Dwina,
the Moscowa, the Dneiper, the Beresina, &c., in the campaign of 1812;
the repairing of the bridge near Dresden, and the passage of the Elbe in
1813, &c.

_Rafts_ formed of timbers, casks, barrels, &c., are frequently used as
military bridges. They may be made to bear almost any weight, and will
answer for the passage of rivers of any depth and width, provided the
current be not rapid.

Where the bridge is to be supported by rafts made of solid timbers,
these timbers should be first placed in the water, to ascertain their
natural position of stability, and then the larger ends cut away on the
under side, so as to present the least possible resistance to the action
of the current. They are afterwards lashed together by strong rope or
withe lashing, or fastened by