Fortification, Permanent

Permanent fortification, as opposed to temporary or field fortifications, were meticulously designed and constructed over long periods of time using durable materials that could withstand the destructive effects of weather for decades or, in many cases, centuries. Due to the heavy burden this type of fortification placed on a nation's resources, permanent fortifications were generally only used to defend strategic points of lasting value and were habitually sited on commanding points of ground that a hostile attacking army could not avoid. Prior to the beginning of the nineteenth century it had been considered sufficient to defend strategic points by surrounding them with walled enclosures that were high enough and thick enough to both prevent open assaults and defilade the interior side of the wall from direct artillery fire. These enclosures were themselves defended by a coordinated pattern of outworks designed to compel a hostile army to fight through a succession of mutually supporting fortifications before its advance could reach and breach the enciente. In some cases the line of outworks were defended by advanced works positioned on ground at a distance from the walled enclosure that could be turned to an attacking army's advantage.

The most notable and impressive feature of permanent fortifications constructed before the last quarter of the nineteenth century was the massive masonry walls constructed to form a fortification's enciente or fortified enclosure. Their primary purpose, when combined with other elements of a fortification's profile, was to present an almost insurmountable barrier to open assaults. A height of about 24 to 30 feet was generally considered sufficient to discourage even the most over-zealous enemy from attempting to storm a fortified place by escalade. If a permanent fortification could not be taken by open assault, then a hostile army would necessarily be compelled to either blockade it in hopes of eventually starving the garrison into submission or conduct an attack by regular approaches with the object of breaching the enciente wall and opening the fortification to an assault.

Three basic types of masonry walls were used to establish the walled enclosures of permanent fortifications: revetment walls, casemated shield walls, and detached (and semi-detached) walls. Revetment walls were used in combination with large earthen ramparts; the revetment lined the exterior side of the rampart, held it at an unscalably steep angle, and provided a hardened shell that could only be breached by persistent artillery fire or mining operations. Revetment walls were usually extremely thick and were reinforced and bonded to the earthen rampart by counterforts. Casemated shield walls were generally hollow with the interior side of the walls broken into a series of vaulted gun chambers. In this case the shield wall was pierced by embrasures and loop-holes that allowed artillery and small arms fire to pass through the wall. Detached and semi-detached walls were free standing walls placed in front of an unrevetted rampart. In most cases these were crenellated or pierced with loop-holes for small arms at regular intervals.

These massive stone and brick walls were the basic structural feature that separated permanent fortifications from field fortifications, they allowed commanding ground that defended strategic points to be occupied permanently without the need to rebuild the work every few years. Where earth and timber field fortifications would deteriorate after the passage of a few months as the wood rotted and erosion destroyed its defensive structures, masonry walls built on sound foundations remained in place and constantly ready to receive an enemy's attack. This quality of permanence also imposed greater circumspection in the design and construction process; field fortification could be constructed with little or no immediate expense in a few days, abandoned when no longer required, and another built again if the situation required it. But the massive amount of time, material, and labor required to construct a permanent fortification the chances that future events would turn the expense of its design and construction into an unfortunate waste of resources. A temporary work might be re-designed and modified by re-arranging a few mounds of earth and hauling in a few wagon loads of fresh timber, but once the foundation of a permanent fortification's walls were laid, there was little that could be done to alter the design or adapt it to meet advances in technology and changing political situations. Permanence imposed caution in the selection of a fortification's site, its design, selection of appropriate materials, and its construction.

Common historical opinion tends to suggest that the long series of wars in Europe at the end of the eighteenth and beginning of the nineteenth centuries put an end to the usefulness of permanent fortifications for the defense of strategic points. Large armies seemed to be able to ignore fortifications at will by masking and maneuvering around them; fortresses that had once stopped even the most determined armies of invasion seemed powerless once the field army that protected them suffered a decisive defeat. This was nothing really very new; defeats in the field had a tendency to lead to the rapid capitulation of minor fortifications exposed to an enemy's rapid advance in pursuit of the defeated army. Many engineers concluded that the problem was not that permanent fortifications were obsolete or that they could not adequately defend strategic points, but that the style of fortification that had formerly been used was not particularly effective and had to be altered and expanded. Prior to the beginning of the nineteenth century permanent fortifications tended to be constructed around important towns and cities; while their object may have been to control an important invasion route, their only real effect when confronted by mass armies was to interpose a barrier between the city and the ground around it that was occupied by the enemy.

This defect in old style fortresses was remedied by abandoning the idea that a single, relatively small, walled enclosure was capable of both defending a strategic point and influencing the maneuvers of a large hostile field army that could almost always mask the fortress and find a road around the place and continue its operations. Engineers came to the conclusion that the best way to re-establish the unavoidability of permanent fortifications was to create systems of mutually supporting detached defensive works that were positioned at a distance from the strategic points that they defended. Sited on commanding points of ground along important routes leading into or around the strategic point, each detached was designed to both defend itself and participate in the defensive of nearby fortifications in the system. If necessary, these detached works could be connected by lines of temporary works and converted into intrenched camps defended by whatever field forces could be gathered for the defense of the strategic point. The challenge to permanent fortifications presented by large field armies and improved road systems was answered by increasing the number of permanent fortifications intended to defend a place and extending them outward to influence a hostile army's ability to avoid them.

German, Prussian, and Austrian engineers responded to the apparent impotence of permanent fortifications by partially abandoning the bastion system and adapting the principles of the polygonal system to increase fortifications' powers of resistance. Unlike the bastion system, which assumed that the musket would be the primary weapon for close defense of the work, the polygonal system relied on artillery to both defeat an enemy's attacks by regular approaches and provide flanking fire for close defense. A weakness of the bastion system was that most of a fortification's artillery armament was positioned along the parapet at the top of the rampart where it was vulnerable to ricochet fire and could be silenced by an attacking force's siege batteries. The polygonal system attempted to remedy this defect by placing the majority of a fortification's artillery in casemates where, it was supposed, most of the guns could survive the enemy's initial attempts to silence them. By placing casemates in tiers along the full length of a hollow shield wall, it was also supposed that the defenders might be able to maintain a sufficient fire superiority over the attacking force's siege batteries that the attacking army's approaches could not advance beyond the first or second parallel. Depending on artillery for flank defense also allowed an extension of the length of fronts of fortification; this would both provide the defense with more space for more casemated guns and compel an attacking army to lengthen its parallels to envelop the attacked front while spending more time and resources developing its siege works.

These developments in permanent fortifications were not universally accepted. French engineers tended to take what they could from any system and adapt theory to practice while maintaining a general adherence to the viability of the bastion system. Fortifications constructed in the nineteenth century for the defense of important cities such as Paris and Lyon combined detached permanent fortifications with continuous encientes; individual fortifications often combined the advantages of both the bastion and polygonal systems. Sea coast fortifications designed and constructed after the end of the War of 1812 in the United States adapted the polygonal system's tiers of casemates to increase the number of guns that could be brought to bear on shipping while maintaining the bastion system's method of landside and flanking defense. The polygonal system's use of detached and semi-detached crenellated walls also gained some popularity and were designed into some of the later Third System fortifications.

January, 2004

September, 2005