Fortification, the art of increasing by engineering devices, the fighting power of troops who occupy a position. The great improvements lately made in the construction of heavy guns have rendered it necessary to revise the systems of fortification formerly in vogue. Iron and steel turrets are taking the place of masonry on low sites which are much exposed and where earth cannot be employed advantageously. These turrets are revolving cupolas, with spherical roofs; while in some instances the guns are mounted on disappearing carriages. In the United States the frontiers exposed to attack being very largely maritime, the fortifications are principally batteries of heavy guns adapted to a contest with steel-plated ships. These are inclosed in the rear with a land front, as protection against a land attack, but not made sufficiently strong to stand a long siege, it being taken for granted that reinforcements can quickly be provided to repel a besieging force. It was formerly usual to mount guns in masonry casements built tier over tier, this method of building being common throughout the world. But this method has been discarded in consequence of the modern development of ships and guns. The system recommended by a board of military engineers, in 1886, proposed the use of steel turrets, armored casements, barbette batteries, mortar and floating batteries, and submarine mines; but so rapid has been the advance of military progress that the plan outlined by that board has been very largely modified in recent constructions, it having been found that, all things considered, earth and sand constitute the most effective defense.
Iron-clad forts. -- For nearly an entire generation -- ever since 1859 -- the progress of fortification in Europe was in the direction of the use of some form of iron armor. In England the necessity for using iron in fortifications was apparent just as soon as this material began to be used in ships, and in 1861 England entered upon the work of rebuilding her forts with iron. It was substantially completed in 1878, at a cost of $37,000,000, expended on nine harbors. Within the last few years have come the solid iron turrets, of enormous thickness, carrying two 80-ton guns each, which form part of the defense of Dover, England. While many of these forts, which were built while the contest between guns and armor was still in progress, can be pierced by the more recent guns, yet the number of large guns which they mount is far superior to the number that could be brought against them afloat, and in connection with torpedoes and ironclad ships they afford a secure defense.
Entry from Everybody's Cyclopedia, 1912.