These batteries are all nearly alike in the general principle of their. construction. They consist primarily of an epaulernent, or built-up shelter, behind which the guns are placed; the platform on which the guns actually rest may or may not be above the ordi nary level of the ground, according to the nature of the battery. The epaulement or parapet is of immense thickness, to resist the action of the enemy's cannonballs. The thickness at the top is seldom less than 12 ft., and may be as much as 20; for it is found that a 24-pounder ball will penetrate 18 ft. of earth. The guns are placed about 20 ft. apart, behind the parapet. Some batteries are straight, with all the guns parallel; while others may be portions of a triangle (redan) or a polygon, and the earthwork has to lie con structed accordingly. There is generally a ditch from 12 to 20 ft. wide, outside the earthwork; and the depth from the crest of the parapet to the bottom of the ditch is 12 to 16 feet. For gun and howitzer batteries, there are embrasures through which the firing takes place; but mortar batteries are without those openings.
Sometimes the epaulement is thrown up loosely, in haste; but for the better kinds of batteries, fascines, gabious, and sand-bags are largely employed. The main structure is lined with fascines 9 ft. long, and the embrasures lined with other fascinel 18 ft. long 40 or 50 of the two kinds being required per gun. The fascines here spoken of are long bundles of brush-wood, weighing 30 to 200 lbs. each. Sometimes sand-bags are used instead of fascines, each containing about a bushel of sand or earth; and sometimes gabious, which are wicker cylinders filled with earth. A 6-gun saud-bag B., made wholly of these materials, requires nearly 8000 sand-bags.
The fate of a field B. often decides a battle. At the battle of the Alma, when once the guards and highlanders had reached the Russian batteries on the hill, the day was won. At the battle of Inkermann, the issue depended mainly on the possession of a small 2-gun sand-hag 13., which remained, after many vicissitudes, in the hands of the allies.