For as long as man has required protection and prestige he has built fortifications. Put simply, the art of fortification consists of the combination of terrain with available materials to form defences, and siegecraft concerns the attack of these fortifications. Throughout history there has been a changing balance between attack and defence as technology and tactics swing the advantage first one way and then the other. There are numerous examples of sophisticated fortifications from prehistory. Most consist of an earthwork or ‘dun’, which developed into the complex Celtic hill forts, the best example of which, Maiden castle in Dorset, comprises three sets of concentric banks and ditches, surrounding a wall and palisade. The gates were protected by an ingenious system of re-entrants and switchbacks, designed to lead any attacker backward and forward under a rain of missiles. We know that these were usually slingstones, as great piles of them have been found stored in convenient places.
Where the terrain was rocky, the inhabitants were forced to build upwards instead of digging into the earth. Stone forts or cashels can be found dotted all over Ireland and the Western Isles, comprising three rings of walled enclosures, in between which were to be found fiendish spiked obstacles that resembled the later chevaux-de-frise. Dun Aengus on the Isle of Arran is a prime example of this kind of fort. Indeed, mainland Scotland boasts some very unusual prehistoric fortifications, built like towers without mortar, and known as brochs. These refuges would be built on a peninsula, with access guarded by a series of ditches.
But it is to the ancient Near East and the lands of the Bible that we must turn to discover the origins of fortification. The walls of Jericho, the oldest city yet to be discovered, were built about 7000 bc, enclosing a permanent natural spring, valuable enough in itself to be worth defending in that arid climate. Ten different cultures subsequently inhabited the site, but the most famous monuments they left were a great tower 30 feet (9.1 metres) high, and a wall 6 feet (1.8 metres) thick, with a ditch, encircling the city, or rather a series of walls built and rebuilt over centuries, eventually forming a great mound or ‘tell’. All this dates to some 6, 000 years before Joshua, who must have laid siege to Jericho in about 1500 bc. A similar preoccupation with defence can be seen at Çatal Hüyük in modern Turkey dating from 6500 bc, where the houses are packed tightly together and only accessible by a narrow entry in the roof.
By 1200 bc the Egyptians were using crenellated walls such as the ones found at Medinet Habou. We know a considerable amount about Egyptian siege techniques from surviving accounts of Tuthmosis' seven-month siege of Megiddo, where he captured at one fell swoop all the princes from the surrounding area so ‘the capture of Megiddo was the capture of a thousand towns’.
The Assyrians were the past masters of fortification and siegecraft. They developed a startling variety of machines and equipment for assaulting enemy defences including catapults, storming towers, rams, and mines (see siege engines). These techniques remained largely unchanged until the introduction of gunpowder. Assyria's expansionist policy created the need to constantly reduce fortified population centres that resisted the Assyrian yoke. An earth ramp was used to bring a metal-tipped battering ram into position. To prevent the defenders dropping rocks or burning materials onto it, the ram was often housed with an elaborate canopy, and continually doused with water. Propaganda and the threat of fire and the sword was used to encourage capitulation. Blockade was a commonplace technique, and in many of the areas that the Assyrians conquered water was scarce and so fortresses usually included large underground cisterns to help them resist a siege. With their ruthless and efficient approach, the Assyrians were able to take Jerusalem in less than a year in 701 bc, but the city of Arpad held out for three years against Tiglath-Pileser, and Nebuchadnezzar took a colossal thirteen years to take Tyre, a stronghold that was destined to cause a later conqueror some inconvenience too.
The Romans were engineers par excellence and this applied to their conduct of siege warfare. Caesar describes in detail all the preparations for and his conduct of the siege of Alesia against Vercingetorix the Gaul in 20 bc. The Romans were fond of building enormous ramps to allow them to walk over the walls of an enemy's strong point. This was used to singular effect at Masada in the winter of ad 72-3; like most Roman sieges the capture of Masada was achieved by the shovel. A gigantic earth ramp, which still remains, was constructed to bring siege engines up to the rocky plateau. The Romans also specialized in extensive frontier works such Hadrian's wall in the north of England and the Antonine wall in Scotland. Indeed, the whole defence of the late empire was based on a series of frontier forts or limes, and coastal forts such as those found on the so-called ‘Saxon Shore’ in England. The best example of a fort of this type is at Pevensey. However, these forts and walls were only as good as the garrisons that served them, and relied on field armies to contain any penetration, and without reliable troops to defend the boundaries of empire the barbarians were free to pour through unmolested.
The art of fortification was lost in the West for many years after the collapse of the Roman empire, and local strongholds relied on stout stockades for defence. Settlements would grow up around these defended localities and their garrisons, and the regional war leader would offer military protection from marauders, such as the predatory Vikings and Magyars, in return for agricultural labour on the surrounding lands. This is essentially what developed into feudal service. These wooden refuges or keeps were developed into the motte and bailey castle, the bailey being the courtyard and the motte being a large mound of earth on which sat the inner refuge or keep. In time the wooden construction of the keep was replaced by stone or masonry, becoming bigger and more grandiose as the barons acquired wealth, fame, and influence. Experience of campaigning in the Crusades from the 11th to the 13th centuries resulted in the import from the East of the concentric castle plan, which was the high point of medieval stone fortress design. It was found that circular towers in successive rings, linked by curtain walls, offered better defence and deflected missiles from the great stone-throwing engines or trebuchets, another import from the Middle East. Major strongholds such as Krak des Chevaliers in Syria, and the English castles in Wales—Conwy or Caerphilly, for example—were pretty much impervious to direct assault, and had to be starved into submission or undermined by the extensive digging of tunnels. These tunnels were usually beneath walls or towers in chambers which were packed with combustible material and fired. In 1215 King John's miners brought down a corner of the great keep at Rochester. ‘We command you’, he had written to his justiciar, ‘that with all haste, by day and night, you send to us 40 bacon pigs of the fattest and less good for eating to bring fire under the tower.’
The development of siege artillery in the 15th century necessitated a complete revision of fortification, for high stone walls crumbled under the repeated impact of cannon balls. In 1494 Charles VIII of France conducted a lightning campaign in Italy, taking fortress after fortress by means of a truly modern siege-train consisting of accurate guns capable of repeated and rapid fire. Artillery fortification was born in Italy in around 1503, as a reaction to these new weapons. This new system, the trace italienne, was based on mathematical and geometric principles and coincided neatly with the rediscovery of science and technology associated with the Renaissance. It developed into the geometrical fortification associated with engineers like Vauban and Coehoorn, and had real impact on war from the late 16th century onwards, with generations of engineers, like Montalambert and Cormontagne, making their own additions to a branch of military science which assumed the fiercely contested complexities of theology.
The fearful geometry of fortification and siegecraft reached its peak with the systems associated with Vauban. However, the defensive and offensive systems actually built were often much simpler and more tailored to the terrain than the idealized examples shown in text books
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Quintessential to the system was the bastion, a four-sided work shaped like an arrowhead, which jutted out in front of the main line of ramparts. The guns on its two faces fired out across the glacis, a carefully sculpted open area between the fortress and the countryside beyond, and those on its two flanks swept the fronts of the ramparts with enfilade fire. Guns usually stood on a flat terreplein, shooting over a wide earth parapet which was intended to absorb incoming fire, although they might also fire through splayed embrasures, or be housed in vaulted casemates on a lower storey. Between the bastions ran the curtain, the main wall of the fortress. Like the bastions it had a carefully planned profile to ensure that the attacker had no vulnerable masonry to engage: from his viewpoint, the ramparts just showed above the glacis. The fortress side of the glacis ended with a palisade protecting a covered way, along which defenders could walk, and then dropped down into a deep, wide ditch which might, according to local circumstances, be wet or dry. Detached works called ravelins or (from their appearance) demi-lunes (half-moons) often stood out in front of the curtain between the bastions, and sometimes extra works formed an extra outer skin of fortifications. Excellently preserved examples of this type of fortress can be seen at Naarden in Holland, Le Quesnoy near Lille, Neuf-Brisach in Alsace, and Berwick-on-Tweed in Britain.
The attack of these fortifications was scarcely less methodical than their design and construction. A lucky attacker might gain admittance by a ruse or overwhelm unprepared defenders by a sudden assault. But he would usually have to mount a formal siege, first opening a trench line parallel to the defences and just out of range of their guns, and then sap forward, digging zigzag trenches to open a second parallel, and later a third. Meanwhile his gunners would concentrate on hostile pieces on the front under attack, and would also try to drop mortar bombs into the body of the place: in 1717 a mortar bomb hit the main Turkish magazine at Belgrade, causing an explosion which killed 3, 000 people. The defender might mount a sortie, but this would probably do little more than buy time. Eventually the attacker would assault the covered way, and having established a lodgement there would set up breaching batteries mounting heavy guns which would pound away at the foot of the scarp wall supporting the rampart. When this tumbled into the ditch, establishing a practicable breach, he would summon the fortress's governor to capitulate. A prudent governor usually complied, for if the attacker was compelled to mount an assault through a defended breach his maddened soldiers could not be expected to grant quarter to the garrison or to respect the property or chastity of the inhabitants. Mining, with gunpowder now replacing the pig-fat of yesteryear, might accelerate the process, but a wily defender would have prepared countermine galleries of his own, and a wet ditch presented particular problems.
With the introduction of effective rifled and breech-loading weapons in the 19th century, and subsequently high-explosive shells, the advantage swung to the attacker who could now overwhelm most defences with devastating firepower. The Union army rapidly captured the large and complex work of Fort Pulaski in Georgia in 1862. However, this did not signal the end of masonry fortifications, for a line of forts nicknamed ‘Palmerston's follies’ was built in the 1860s to defend the British naval base of Portsmouth against attack from its landward side, and after the Franco-Prussian war Sere de Rivières fortified the Franco-German border. Masonry was protected by concrete, often with a ‘burster layer’ of sand between the two to absorb the explosion of shells, and guns were protected in steel cupolas like those favoured by Brialmont. As the range of artillery increased, so engineers built outlying forts to keep an attacker out of range of the body of the fortress, and key sites like Liège, Namur, and Verdun had rings of forts surrounding them.
Improvements in firepower enabled infantry in field fortifications to play an increasing part in defence. The fortifications of Petersburg in the American civil war were ramshackle, but they gave the Union army pause for thought, and infantry played their own lethal part in the fighting around Plevna in the Russo-Turkish war of 1877-8 and Port Arthur in the Russo-Japanese war of 1904-5.
In the opening moves of WW I fortresses at Liège, Namur, and elsewhere were smashed by the fire of heavy howitzers. Continuous lines of field fortification faced each other on the western and to a lesser extent the eastern front, and dealing with the locked front became the war's principal tactical problem. When reviewing the dreadful impact of the war, it was not unreasonable to conclude that the defensive was the stronger form of warfare, and for the French to note that Verdun forts—ludicrously under-gunned though they were—had coped far better with months of bombardment, sometimes by the heaviest guns available, than might ever have been expected. Taking these lessons to heart the French built an extensive permanent defence system, the Maginot Line, between the wars, but the northern end of this line resting on the Belgian border was left lightly protected, and it was this gap that the Germans were able to exploit in their campaign of 1940.
Fortifications were extensively used in WW II, but the essentially fluid nature of the fighting made fixed fortresses like Singapore, the Atlantic wall, and the complex of Belgian forts around Antwerp and Maastricht, something of an anachronism. The combination of artillery, tanks, and air power co-operating with infantry and combat engineers, meant that most fortresses would eventually succumb to determined assault by well-trained troops. Indeed, in 1940 the supposedly impregnable Belgian fortress of Eben-Emael was taken by 78 German paratroops in something under half an hour of intense fighting. Examples of less ambitious fortifications abound, like the concrete pillboxes, often hexagonal, which dot southern England. The Germans constructed huge fortifications along the French coast—the ‘Atlantic wall’—using forced labour. These installations were key targets for air attack, naval bombardment, and the first troops ashore in the Normandy campaign.
Since WW II extensive fortifications have been seen in use in the Korean war in 1951 and the Bar-Lev Line along the Suez Canal on the eve of the Yom Kippur war, as well as temporary fortresses such as the firebases of Dien Bien Phu in Indochina and Khe Sanh in Vietnam. Moreover, permanent fortifications have been widely used for civilian and military nuclear defence. Ballistic missiles are housed in deep concrete and steel reinforced silos, which has necessitated the development of special missiles intended to burrow deep and detonate far underground in an attempt to defeat them. Hardened aircraft shelters and weapons storage bunkers are also permanent fortifications, as are deep command bunkers such as the war headquarters built at High Wycombe in England or Strategic Air Command's headquarters beneath Cheyenne Mountain in Arizona.
Fortification from its origins as a response to a need for security in an uncertain world, developed into a matter of statecraft and diplomacy, and a reflection on international circumstances. Throughout time there have consistently been misunderstandings as to the nature and purpose of fortifications, and some of the faith placed in their effectiveness has been unjustified. They still represent, as they always have, the endless duel between attack and defence, between immobility and manoeuvre. Considerations of force protection, so important in the 1990s and beyond, will encourage their construction, notably to defend logistic bases, surveillance systems, or ports of entry. Conversely, attackers will ponder technical or tactical means of attack: plus ça change.
Bibliography
- Connolly, Peter, Greece and Rome at War (London, 1981).
- Duffy, Christopher, Fire and Stone: The Science of Fortress Warfare 1660-1860 (Newton Abbot, 1975).
- —— Siege Warfare: The Fortress and the Early Modern World 1494-1660 (London, 1979).
- —— The Fortress in the Age of Vauban and Frederick the Great 1660-1789 (London, 1985)
— Toby McLeod/Richard Holmes
