In even the earliest and most primitive societies, the need to stave off attackers led to the construction of defensive physical structures.

In even the earliest and most primitive societies, the need to stave off attackers led to the construction of defensive physical structures. The variety of such responses naturally became ever more diverse as groups worldwide had to meet the intersecting challenges of the foe, their own resources, climatic and geographical constraints, and anticipated forms of organized violence. Fortification is thus any construction, permanent or transitory, earthen, organic, or stone, designed to shield defenders from an attacker while those defenders either await help or resist assaults themselves. Even with the rather limitless bounds of human ingenuity, fortifications nonetheless tend to fall within four somewhat interrelated categories: refuges, strongholds, fortified lines or zones, and urban walls.Fortifications;medievalFortifications;medieval

By 500 c.e., each type of fortification had appeared numerous times in human conflicts. A Strongholdsstronghold differs from a Refugesrefuge in that it is a place that hosts an active defense; from its walls, defenders may launch offensive sallies. The refuge, by contrast, is primarily defensive, a place to wait out the enemy in such a position of strength that the enemy will forgo the costs of attack. The final types of military architecture are even less distinct; city Walled citieswalls are in one sense fortified lines. Here, though, the concern is with those fortified zones meant to secure the peace of whole regions.

All types appeared concurrently and in overlapping cycles of need and development worldwide before Europe’s medieval period. The Roman Empire had its own strategic mix of city Wallswalls, fortified frontiers, and the near-instant fortress otherwise known as an encamped army. After the Empire’s fall in Western Europe, its legacy continued in the walls that surrounded many cities, the fortified zones of northern England and the Rhine and Danube Rivers, and the defenses of Constantinople, which stymied and stupefied many an invader. In Asia the tradition of long walls was already centuries old, having been initiated by the first Qin emperor in 221 b.c.e. In the Americas, the lack of metallic technology severely constrained the forms warfare might take; moreover, the earliest Mayan societies may well have not had, in the traditional Western sense, cities to defend. In sub-Saharan Africa and Australasia, the archaeological record has been less forthcoming. Doubtless, the inhabitants shaped earth as needed into ditches and ramparts, the latter surmounted even today by thorny hedges, known as bomas or zarebas, to keep out predators.

Despite Fortified linesthe remaining fortifications that surrounded them, the Europeans of the Germanic West had difficulty reaching the level of defensive sophistication of the Roman Empire. Even with the extant physical reminders of the Roman fortified lines, especially Hadrian’s Hadrian’s Wall[Hadrians Wall]Wall in Britain, they declined to maintain such lines and delayed a long time building their own. Perhaps they saw little point to such defenses, which had failed to keep them out of the Roman heartlands. The permeability of such zones has raised a number of debates as to their real purpose, and whether they were meant to prevent invasion, to slow invaders, or to keep internal populations within limits. The Saxons, who invaded Britain after the 450’s, found the defenses of the Saxon Saxon ShoreShore did little to slow their conquest. To the north Hadrian’s Wall likewise hindered the Picts little in their raids.

Hadrian’s Wall stretched for 117 kilometers across northern England, ranging in thickness from 2.3 to 3 meters and averaging a height of from 5 to 6 meters. The wall was part of the Roman strategy of defense in depth. In the absence of manned watchtowers and fortified camps to the rear, the Saxons were hardly set to use the wall to its best advantage. Even so, the wall did form, in its less than pristine state, something of a hindrance to the return of raiders northward. Northumbrian pursuers could count on it slowing marauders if those raiders tried to get their spoils through or over the fortifications.

It would appear that Offa’s Offa’s Dyke[Offas Dyke]Dyke, built during the reign (757-796) of that Mercian king, was meant to achieve an effect along the Welsh border similar to that of Hadrian’s Wall. An earthen rampart 18 meters wide formed in part by the ditches that bracket it, Offa’s Dyke meandered for 192 kilometers through regions that had little in the way of leftover Roman defenses or roads. There was little hope of keeping out Welsh Welshraiders, especially since the dyke was virtually unmanned. Again, though, its physical bulk would slow the exodus of such raiders, especially if they were driving stolen livestock, permitting Mercian forces to catch up with the marauders. In addition, the dyke provided a roadway that cut across the ranges and rivers of the Welsh marches, thus easing both the report of such raids and the speed of reaction.

The impassability of terrain might make fortified lines not only a cost-prohibitive measure but also a rather unnecessary one. In Mesoamerica contending empires could keep invaders at bay simply by blocking well-established paths. In the absence of siege equipment and draft animals, such structures would not have needed much complexity to be effective. In Europe fortified bridges developed not only to secure lines of communication and transport but also to block the progress of Viking Vikings;raidsraiders up the river systems. Thus a number of such bridges controlled the rivers below Paris after the 880’s to prevent direct access or indirect efforts by portage. When Vikings actually did besiege Paris in 885, it took them over four months just to reach the city.

The most famous and latest of all fortified lines are of course those of China. The Great Great Wall of ChinaWall is not actually a single wall curling along China’s northern borders, nor does its current condition date back to 221 b.c.e. The earliest (Qin) walls were earthen, tamped down by forced labor between retaining wooden walls that connected watchtowers. The actual remains of this wall are now in the realm of conjecture. The current masonry walls–which are actually many sets of walls, not always connected, and not one continuous line–date from the Ming Ming DynastyDynasty (1368-1644) emperors, who reigned after the expulsion of the Mongol Dynasty. The facts of these fortifications are impressive: 2,400 kilometers in length, 7.6 meters high at a minimum, often 9 meters wide, and sometimes scaling 70-degree slopes. Like their European counterparts, however, they proved less than impermeable, again raising the question of whether the walls were more clearly intended to keep the native population contained within and untainted by exterior contact.

As the Germanic groups, especially the FranksFranks, entered the deteriorating Roman Empire, they brought a new structure to the landscape: the private fortress. Although these small Refugesrefuges, which utilized so little stone, have left few archaeological remains, contemporaries noted their appearance in rural and isolated areas. Most important, commentators of the day stressed the remoteness or inaccessibility of such sites. Because of the new inhabitants’ rudimentary technology, these protocastles relied on their physical surroundings to deter would-be invaders. On isolated summits, crowning precipitous sites, these forts gave some protection to the rural regions of Gaul and Visigothic Spain; their small size and private ownership, however, limited their value as refuges for a harried populace. Instead, the later Frankish kings found them to be troublesome centers of resistance, because it was so difficult to bring an army to bear on such places.

The twelfth century attack and defense of a city wall, with numerous types of siege engines in use.

(Library of Congress)

The situation differed in eighth and ninth century Anglo-Saxons[Anglo Saxons]England;Viking raidsAnglo-Saxon England, especially Wessex. By the 870’s, after Viking invaders had occupied much of England and pushed into Wessex, King Alfred the Alfred the GreatAlfred the Great (king of Wessex)Great (r. 871-899) secured a truce after his victory at Edington, Battle of (878)Edington (878). During the cessation of active campaigning, Alfred devised a sophisticated defensive strategy centered upon thirty-three refuges. These Burh (Anglo-Saxon fortification)burhs, as they were called, were scattered over the kingdom, seldom more than a day’s ride apart, and usually near major transportation routes. Often quite sizable and well provisioned, the burhs were meant both to house a large garrison and to provide ample room into which a refugee population might flee. Alfred’s strategy, which would prove successful in 896, was to have the population and movable wealth protected in the burhs while he shadowed the invading Vikings with the Wessex army. By hampering the Vikings’ ability to forage or pillage, Alfred simply made his kingdom an uninviting prospect to Viking plunderers.

These fortifications did not have to be terribly complex, because the Vikings had little in the way of siege weaponry. Nonetheless, Alfred’s administration prepared the burhs well, as is known from a document called the Burghal Hidage (c. 920), which lists them. By dividing the resources of the kingdom into units called hides, each of which was sufficient to provide one man for burh garrisons, the Anglo-Saxons assigned enough hides to each burh to assure that its walls were defended by one man for every 1.3 meters. Because some burhs had circumferences of over one mile, this meant that Viking invaders had to sense the sizable numbers of uncowed foes they left in their wake as they bypassed the burhs. The burhs themselves were formidable: The first barrier was an exterior ditch perhaps more than 30 meters wide and sometimes as deep as 8 meters; an earthen bank came next, reaching up to 3 meters in height; timber defenses surmounted this ringwork in most cases, but stone walls were put in place at major sites, especially those that housed the royal mints. Many burhs took advantage of natural defenses, such as swamps and rivers, whereas others were built upon the remains of previous Roman fortifications.

The advantages offered by burhs or even the most simple defenses naturally drew people to those fortified locales. This rationale appears to explain the growth of the stone enclosures at Great ZimbabweAfrica;ironworkingZimbabwe centuries later. The original impetus for the southern African plateau’s settlement remains debated, but the availability of iron doubtless held part of the appeal. At all three parts of the site, the most restricted sites are those where archaeology has found iron stores or iron-working tools. Between 1100 and 1500, the Great Great Enclosure (Great Zimbabwe)Enclosure was built, with walls of quarried granite about 10 meters and without any mortar, encompassing first a hilltop and later a site across a small valley. Early in the twentieth century, the archaeological record at Great Zimbabwe was greatly altered or nearly destroyed, and the reason for the site’s abandonment by 1700 is unknown. However, no one has supposed a victory by besiegers.

The Strongholdstransition in Europe from simple refuges to Castles;timbercastles came with the motte-and-bailey Motte-and-bailey structures[Motte and bailey structures]structure, whose origins lie in the tenth and eleventh centuries. The heart of this fortification was the motte, a steeply conical mound surrounded by a ditch and crowned by a timber palisade. Within this enclosure, a wooden tower originally rose, most often on stilts. The bailey was a secondary enclosure at the base of the motte, somewhat kidney-shaped as it fit alongside the motte. Separated from the motte by ditches and protected by its own palisade and ditches, the bailey formed a living area and an extra line of defense. From the bailey, a Bridgesbridge either spanned the ditch on a more convenient gradient to the motte’s gate or reached only to steps cut into the motte’s steep slope. If the bailey became lost to attackers, the bridge was easily disposable. The quick proliferation of the motte-and-bailey lay in its most basic advantage: It provided a maximum amount of defense at the lowest cost of construction. Moreover, it was possible to build one within days.

In addition to its defensive capabilities, the motte-and-bailey had an offensive potential. As an easily built, forward base for troops, mottes were useful in subduing hostile regions. One of the earliest builders of mottes, Fulk Fulk IIIFulk III (count of Anjou)[Fulk 03]III (c. 970-1040), the count of Anjou, used castles to push his borders farther toward Normandy. In turn, the Normans learned from this tactic and applied it most dramatically in the conquest of England. William the William the ConquerorWilliam the Conqueror (king of England)Conqueror (c. 1027-1087) built motte-style fortifications immediately upon his arrival in England, a fact graphically illustrated in the Bayeux Bayeux tapestrytapestry. After his victory at the Battle of Hastings, Battle of (1066)Hastings (1066), William and his chief followers brought the whole of England under control by establishing motte castles at crucial points throughout the kingdom. After the transition to stone castles became widespread in the twelfth century, many mottes did not have the stability to support massive keeps as replacements for the wooden towers. Instead, the palisade was rebuilt as a “shell keep,” so that the weight of the new masonry was dispersed over the mound.

Although the use of timber castles continued into the thirteenth century, the transition to Castles;stonestone appears to have begun in the late tenth or early eleventh century, owing in part to the innovations of Fulk III. Some scholars have convincingly argued that the bulky, rectangular towers at Langeais and Montbazon, reaching to 16 and 30 meters high respectively, were Fulk’s constructions and that Fulk may well have been responsible for a number of other stone castles in the region. Not surprisingly, many of the stone castles surrounding Anjou date from soon after this period, as Fulk’s rivals and successors imitated his new building program. These new keeps, or Donjonsdonjons, were massive, multistoried edifices that could house many troops. Fulk’s two towers had walls between 1.5 and 3 meters thick and up to 30 meters high. The White White Tower (London)Tower in London, begun by William the Conqueror, had walls as thick as 4.5 meters and as tall as 27 meters, with the corner turrets reaching above that height. It comprised 30 square meters, and the keep at Colchester was even larger.

The new preference for such expensive and mammoth constructions physically reflected the increasing wealth of the feudal nobility as principalities such as Anjou, Normandy, and of course, England, stabilized. The ability of these lords to command greater resources also meant they could put better-equipped armies into the field. Thus the siege weapons of antiquity, which had never completely been forgotten, began reappearing: battering rams, ballistae, onagers, and later, the trebuchet, as well as the old standby, fire. Successful defense against these weapons required the use of stone. The spread of castles was dramatic: The French province of Poitou had only three castles before the Viking incursions, but at least thirty-nine castles dotted the province by 1100. No archaeological evidence has been found of castles in the northwestern region of Maine before 900; two centuries later there were sixty-two. Other regions saw similar levels of castle-building. Such numbers do not take into account fortified residences, which lacked the defensive power of castles.

The intensified wealth and warfare of Europe did not account alone for the spread of more sophisticated defenses; inspiration came also from Constantinople and the Muslim fortresses taken only with the greatest effort during the Crusades;First (1095-1099)First Crusade (1095-1099). The earliest castles that the Crusaders built were the rectangular keeps to which they had been accustomed in Europe, but the needs of these exposed states and sites soon mandated a change. Larger complexes became the rule in order to house both greater garrisons and the supplies necessary so that such a force could hold out, possibly for years, until relief could arrive from other allies or from Europe. Saphet had a garrison of between 1,650 and 2,000 men, while Margat’s 1,000 defenders were supposed to be able to hold out for five years; the cisterns at Sahyun held ten million liters of water. These fortresses reflected Byzantine Empire;fortificationsByzantine reliance on high, massive walls studded with towers to provide enfilading fire. These walls could actually be built more quickly than one of the rectangular keeps; moreover, they provided space for vitally necessary cisterns and reservoirs. Some castles still had keeps, but these were a final defensive point rather than the primary one.

The most famous of the Crusader castles is Krak des Krak des Chevaliers (castle)Chevaliers, which remains impressive even in its ruined state. Occupying a hilltop in Syria that had formerly been a Muslim stronghold, it began with the advantage of difficult access. Its outer wall was added in the 1200’s even as the inner defenses were strengthened. This wall encompassed an area of 210 by 140 meters and had both semicircular towers and Machicolationsmachicolations, or openings in the overhanging battlements that protected defenders who fired missiles, rolled stones, or dropped combustibles upon attackers at the wall’s base. In forested Europe machicolations were only slowly adopted, because wooden overhangs, or Hoardingshoardings, were so easily built for the same purpose. The higher inner circuit of walls could complement the outer defense with missile fire. Two towers flanked the small gate, which gave access either to the forecourt or to a series of gateways that protected the entrance into the fortress proper. The inner wall, or enceinte, was anchored by five large towers. In addition to these defenses, a massive talus, or sloped base, made the walls on the southern and eastern sides virtually impervious to mining and scaling ladders. Apart from its defensive function, the castle’s increased lower bulk also protected Krak des Chevalier from the earthquakes that had damaged it in the mid-twelfth century. In later centuries, Japanese castles would also contend with natural catastrophe. Below the talus was an artificial reservoir, and granaries and armories lined the walls. Little wonder, then, that the Mamlūk armies that took Krak in 1271 opted to trick the defenders into surrendering rather than risk an unsuccessful siege.

Krak des Chevaliers, in modern Syria, the most famous of the Crusader castles.

(Library of Congress)

The lessons learned in the Middle East soon wrought changes in the structure of castles in Europe. Circular towers came to predominate, as castle builders realized that square angles gave attackers extra blind spots to exploit; more important, curved surfaces resisted the projectiles of pregunpowder artillery better than flat ones. King Richard Richard IRichard I “Lion-Heart” (king of England)[Richard 01]I (1157-1199) of England, also known as Richard the Lion-Heart, would apply this principle liberally at his “saucy castle,” the Château Gaillard castleGaillard, where the exterior wall of the inner bailey had a rippled surface. Although keeps continued to be built, including the huge circular donjon at Coucy, which was 31 meters in diameter, the emphasis moved to multiple lines of defense. Gaillard had three baileys to be captured before attackers faced the keep. Barbicans appeared as new fortifications in front of gateways that provided further fire support for this weakest point in a wall. Concentric walls, with the second overtopping the first considerably, became the new fashion in fortification; towers often broke the continuity of such wall-walks so that one portion of the walls could be lost without losing the entire circuit.

The most distinctive examples of concentric castles were Edward Edward IEdward I (king of England)[Edward 01]I’s (1239-1307) Welsh castles, ten fortresses built between 1277 and 1297. Like their motte-and-bailey predecessors and the Crusader outposts, they had an implicitly offensive function, as their dominating presence and garrisons were meant as continuances of the English king’s campaigns. Edward turned primarily to Master James of St. George, a Savoyard architect, to oversee the project. The show of strength may have been as much in the swift construction of the expensive castles as in the high curtain walls pierced with arrow slits, protective drum towers at each angle, and heavily defended gateways. Only one of these castles had a keep, so the emphasis was on the concentric walls. The inner walls loomed high over the outer walls, so that defenders could fire missiles from both. At Harlech and Beaumaris, the successive gates were sandwiched between flanking towers, whereas the entry itself went through a passage. Attackers within the passage would find themselves at the mercy of Archers and archery;and castles[castles]archers firing through Meurtrières (murder-holes)meurtrières, or Murder-holes[Murder holes] murder-holes.

Although castles would appear during Japan;fortificationsJapan’s Sengoku, or Warring States, Warring States period (Japan)period (1477-1601), they differed markedly from European models in both geographical and cultural considerations. A typical Hirojiro (Japanese fortress)hirojiro, or lowland fortress, had a broad stone base with a curving face which, it was hoped, would offset the threats of earthquake or rain-sodden soil giving way. The towering superstructures above this foundation were actually lightweight wood and plaster, again so built as to survive repeated tremors. Despite the immensity and complexity of Japanese castles, they were rarely the focus of battle, because samurai preferred to display their prowess in the field against individual foes. Such battles also had the advantage of leaving intact buildings to the victor. The Japanese reluctance to adopt Western styles of warfare also meant that artillery had a minimal impact on Japanese castles until the 1800’s.

In very different circumstances, the Maoris (New Zealand)Maoris of New Zealand likewise showed a predilection for ritual combat and the preservation of defenses. The Maori Pa (Maori fortification)pa, the first evidences of which date to 900, seem similar to the motte-and-bailey. At their height, such strongholds often occupied hilltops with difficult access; a wooden palisade surrounded the summit, with ditches in front and embankments within that allowed defenders to hurl weapons upon attackers. The wall was regularly pierced with openings, so defenders could jab spears at those trying to scale the palisade. Close by was a less fortified village whose residents would retreat into the pa when warned by alarms. Long sieges, however, were rare. Attackers would challenge defenders to come out before the pa and engage in single or group combat. If the defenders declined, then a frontal assault might ensue, with the intent of capturing without destroying the fortification and its supplies.

The Walled citiesdefensive importance of cities marked both the beginning and the end of the medieval period. The Romans left a legacy of urban fortification: In Gaul;fortificationsGaul alone, nearly 90 of the 115 cities received new walls, smaller in circumference but imposing still with their 10-meter height, 4-meter width, and foundations reaching from 4 to 5 meters underground. These defenses usually withstood Germanic assaults with ease but were rendered irrelevant if the walls were breached by trickery or treachery. Although rare, a long Siege warfaresiege likewise could succeed by starving towns into submission. These conditions held true throughout the Merovingian period also, and one is reminded that the Crusaders only gained Antioch through bribery. During the Carolingian period, defenses were often neglected or even quarried for other projects, but repairs began anew with the Viking invasions. As towns grew in wealth and population from the 1100’s onward, they had to erect new defenses to safeguard both. This would occur all over Europe, but the most striking example may well be the double curtain at Carcassonne, in southern France, which incorporated lessons learned from the cities of the eastern Mediterranean.

The techniques adopted by European cities may be highlighted by comparison with contemporary settlements in Mesoamerica;fortificationsMaya;fortificationsMesoamerica. Maya centers show remarkable stonework, but it appears that these sites functioned more as royal residences and religious sites than as economic centers. Thus, the majority remained unfortified. Other sites, such as Becan or Mayapán, did have enclosing ditches, large embankments, and wooden palisades, and a few had stone walls topped again by palisades. Sometimes these defensive lines surrounded only core areas of the city. In all cases, however, this military architecture remained rather simple, because besiegers could bring so little weaponry to bear against it.

In Europe, though, the pendulum of innovation was already swinging away from the high walls of concentric castles and cities. Gunpowder Artillery;fortifications forartillery may have been present by 1340, and it made itself felt at the Siege of Calais, Siege of (1346-1347)Calais from 1346 to 1347. Gunpowder weapons became increasingly refined, until they became the primary means of siege warfare. In the early 1400’s the English used them successfully against both Scottish and French cities. More dramatically, in 1453 the land walls of Constantinople, Siege of (1453)[Constantinople, Siege of 1453]Constantinople were breached by Turkish bombards after a millennium of successful defense. The high walls of medieval fortification were now considered a liability, but they could not easily be abandoned. At first, many curtain walls were pierced to admit Cannons;and fortifications[fortifications]cannons to be fired outward, but this had limited success. Outworks (embankments)Outworks began to appear so that defenders could keep besiegers distant with their own cannons. These low-profile embankments foreshadowed the future of fortification. Military architects began to propose a new style of defense: low-profile, wide walls that could hold artillery, even wider ditches to distance besieging artillery, and still more outworks, or Bastionsbastions, to provide flanking fire. Italian cities were the first to adopt this new form of siege warfare. When French king Charles Charles VIIICharles VIII (king of France)[Charles 08]VIII (1470-1498) invaded Italy in 1494, his artillery made a shambles of the medieval defenses in his way, and the Italians adopted the new techniques.Fortifications;medieval

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Ancient Fortifications

Modern Fortifications

Sieges and Siegecraft: Ancient and Medieval