FORTIFICATION, the art of increas ing, by engineering devices, the fighting power of troops who occupy a position. The relation of fortification to the other great divisions of the art of warfare, strategy and tactics, may be divided as follows: Strategy determines the loca tion of the position, which must conform to the general plan of campaign; tactics determines the best disposition of the troops on the position, for offense or de fense; fortification improves the natural features of the position so as to increase the chances of success. Fortifications are commonly divided into two classes: "permanent fortifications" and "field works." Under the former are included all works that are constructed for the defense of town, harbor, arsenal, dock yard, etc., being carefully laid out and built with a view to durability and the resistance of an attack, whenever it may be made; under the latter, all works are classed that are intended to serve a tem porary purpose, such as siege-work and batteries for an attack on a fortress, or lines of intrenchment hastily thrown up for the protection of an army in the field, or to check the advance of an enemy on an important strategical posi tion. These works differ mainly in the manner in which they are built, the ram parts and parapets of permanent works being faced or riveted with blocks of granite; the terre-plein of the rampart on which the guns are worked, the cheeks of the embrasures, casemates, bomb-proof buildings for magazines, etc., being formed of the same material; while field-works consist of mounds of earth formed of that which is thrown up out of the ditch in front, having the ramparts and embrasures riveted with sods of turf, fascines, gabions, and sand bags, the terre-plein for the support of the guns and their carriages being made of pieces of thick timber strongly bolted together.
The great improvements lately made in the construction of heavy guns have rendered it necessary to revise the sys tems 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 ex posed to attack being very largely mari time, the fortifications are principally batteries of heavy guns adapted to a contest with steel-plated ships. It was formerly usual to mount guns in ma sonry casements built tier over tier, but this method has been discarded in con sequence of the modern developments in ships and guns. It was demonstrated during the World War when the Ger mans smashed the Belgian forts that earth and sand constitute the most effec tive defense. Stone, concrete and steel cannot withstand modern siege-guns.
Iron-clad Forts. Since 1859 the prog ress 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 ap parent just as soon as this material be gan to be used in ships, and in 1861 England entered upon the work of re building her forts with iron. It was substantially completed in 1878, at a cost of $37,000,000, expended on nine harbors. Within comparatively recent times have come the solid iron turrets, of enormous thickness, carrying two 80 ton guns each, which form part of the defenses of Dover, England. While many of these forts, which were built while the contest between guns and ar mor 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 con nection with torpedoes and ironclad ships they afford a secure defense. On the Continent the problem was not taken up till guns had reached a greater devel opment, and then it was solved generally in the direction of using iron alone, in the form of turrets or domes. Some were of wrought iron, some of steel, and some of cast iron. The latter were the Gruson cupolas, of which many were constructed in various harbors of Ger many, Austria, Belgium, Holland, and Italy. See FORT.