Guards should be stationed above the bridge, with boats, ropes, grapnels, &c., for the purpose of arresting all floating bodies and drawing thorn ashore, or directing them safely through the _draw_ in the bridge arrangement.
The troops especially charged with the construction and management of the various kinds of military bridges, are denominated _pontoniers_.

The duties of these troops are arduous and important, and, in a country like ours, intersected by numerous water-courses, the success of a campaign will often depend upon their skill and efficiency.
_Sapping_ .-- This is a general term applied to the operations of forming trenches, along which troops may approach a work without being exposed to the fire of the besieged.
In addition to the ordinary sapping-tools, such as shovels, picks, gabion-forks, &c., used in constructing trenches, there will also be required a considerable amount of sapping materials, such as gabions, fascines, sap-fagots, sandbags, &c.
The _gabion_ is a cylindrical basket of twigs, about two feet in diameter, and some three feet in length, and without a bottom.

It is made by driving into the ground, in a circular form, a number of small pickets about an inch in diameter, and of the length required for the gabion.

Twigs are wattled between the pickets like ordinary basket-work, and fastened at the ends by withs or packthread.

Gabions are used in forming saps, batteries, blindages, powder-magazines, and in revetting the steep slopes of field-works.
The _fascine_ is a bundle of twigs closely bound up, from nine to twelve inches in diameter, and from ten to fifteen or twenty feet in length.
The largest are sometimes called _saucissons_.