Fortification, the military art of preparing a place to resist attack.. The means used for this purpose may be those presented by nature, as woods and rivers, or those formed by art, as shelters of earth, wood, or stone, or a combination of both. The artificial obstacles thus used are divided into two classes, permanent and temporary fortifications. When they are of a durable character and the position is to be occupied permanently or for some indefinite period, they belong to the former class; but when the position is to be occupied only for a short time or during the operations of a campaign, they are sometimes constructed in great haste and often of perishable materials, and receive the name of temporary or field fortifications. I. Permanent Fortifications. These are essentially defensive in their nature, and their object has not changed with time. Their history, like that of man, may be divided into three principal epochs, ancient fortifications, fortifications of the middle ages, and modern fortifications.-1. Primitive and Ancient Fortifications. The oldest form of fortification appears to be the stockade, which up to the end of the 18th century was still the national system with the Turks (palanka), and is even now in full use in the Indo-Chinese peninsula.

It consists of a double or triple row of the trunks of stout trees, planted upright and near each other in the ground, forming a wall all around the town or camp to be defended. Darius in his expedition among the Scythians, Cortes at Tabasco in Mexico, and Capt. Cook in New Zealand, all came in contact with such stockades. Sometimes the space between the rows of trees was filled up with earth; in other instances the trees were connected and held together by wickerwork. The next step was the erection of masonry Avails instead of stockades. This plan secured greater durability, at the same time that it rendered the assault far more difficult; and from the days of Nineveh and Babylon down to the close of the middle ages, masonry walls formed the exclusive means of fortification among all the more civilized nations. The walls were made so high that escalade was rendered difficult; they were made thick enough to offer a lengthened resistance to the battering ram, and to allow the defenders to move about freely on the top, sheltered by a thinner masonry parapet with battlements, through the embrasures of which arrows and other missiles might be shot or thrown against the assailants.

To increase the defence, the parapet was soon built overhanging, with holes between the projecting stones on which it rested, so as to allow the besieged to see the foot of the wall and reach an enemy who might have got so far by direct missiles from above. For a similar reason towers, which at first were nothing more than square or semicircular projections, built from distance to distance in the wall itself, were devised, and subsequently were divided into stories, each of which was provided with loopholes to flank the adjacent towers and the straight portions of the wall between them. Each tower could be isolated from the straight portion of the wall adjacent by an interruption at the top, over which communication was had by a temporary bridge. These defences were found to be insufficient against the ingenuity and skill of the assailant, who by means of covered galleries of timber gradually won his way to the foot of the wall, when, by breaking his way through it or undermining it, he overcame or removed the obstruction between him and the assailed. This led to the use of wide and deep ditches surrounding the place, forming a formidable obstacle to the modes of attack then used. When it could be obtained, the ditches were filled with water.

With the decadence of the Roman empire the art of fortification, like other branches of the military art, fell into decay.-2. Mediaeval Fortifications. The principal works that characterize the middle ages are the castles placed in the most inaccessible positions on the lines of communication which the little inland commerce that was still carried on was obliged to traverse. They were provided with every possible device for an obstinate passive defence, being surrounded by a wide and deep ditch or moat, over which a drawbridge was the only communication to the main entrance, which was flanked by towers on the exterior, and closed with massive doors; the winding passage that led into the castle being further secured by a grated portcullis, which could be dropped at a moment's notice to arrest a sudden assault. Loopholes and machicoulis in and on the walls and towers were added. In addition, there was a high interior tower, termed a keep or donjon, which, commanding the exterior, was also a watch tower over the adjacent country. This, the last defensible point, was often provided with a secret subterranean passage, having its outlet in some concealed spot on the exterior, by which succor could be introduced to the castle, or the garrison find safety in a stealthy flight.

The fortifications of towns during this period partook of the same characteristics as those of castles.-3. Modern Fortification. This begins with the invention of gunpowder and its application to military purposes. We divide it into periods according as we find the art practised in Europe. There are four marked periods, viz.: 1, during the 14th, loth, and 10th centuries; 2, the 16th and 17th centuries; 3, the 17th and 18th centuries; 4, from the 18th century to the present time. The first was noted for the rise and growth of the bas-tioned system; it is supposed to have originated in Italy, and was during this period the only one used in Europe, Most of the engineers who superintended the construction of the works were Italians, and it is therefore generally known as the Italian system. The second period was noted for the modifications and improvements in this system made in Holland during its war of independence with Spain. The third period was noted for the improvements made in the bastioned system by the French. The fourth period is noted particularly for the objections made to the bastioned system and the proposal of a new one as a substitute.