FIRE IS A WEAPON of great antiquity. In the form of ‘Greek fire’ it was first brought into use by the Byzantines in the seventh century. They guarded the secret of its composition so carefully that even today scholars debate about the exact nature of its ingredients. All that is known for certain is that it was discharged in liquid form, by a sort of syringe, chiefly as an incendiary agent against wooden structures in siege and naval warfare. It was not ‘fire’ in the modern sense of a propellant or explosive. It was not, for all the fear it aroused and mystery that surrounded it, a very effective innovation. It did not revolutionise warfare, as the coming of gunpowder would do.
Gunpowder nevertheless connects with it, for it is now believed that the basis of ‘Greek fire’ was what the Babylonians called ‘naphtha’ or ‘the thing that blazes’, a seepage from surface deposits of petroleum.1 They found no practical use for it. In China, however, about the eleventh century AD, it was discovered that intermixing naphtha-based substances from local surface seepages with saltpetre yielded a compound that had explosive as well as incendiary properties. The Chinese had earlier stumbled on the discovery that lighting fires, particularly of charcoal, on soils that contained high concentrations of sulphur also produced explosive effects. When purified sulphur was combined with powdered charcoal and crystalline saltpetre — this was perhaps first done for semi-magical purposes in Taoist temples about AD 950 — what we now call gunpowder resulted.2 Whether the Chinese used it in warfare is much disputed. There is no evidence that they made cannon (as opposed to fireworks) before the end of the thirteenth century;3 soon after that date gunpowder was certainly known also in Europe, where its secrets may have been hit upon by alchemists in the course of their eternal and fruitless search for means to turn dross into gold, and where its military utility was recognised as soon as its explosive properties were discovered. Quite how the further discovery was made that, when gunpowder and a projectile were confined within a tube, the force released by detonating the former imparted both range and direction to the latter, defies reconstruction. But it can be dated quite accurately to the beginning of the fourteenth century, since a drawing of 1326 survives that shows a vase-shaped vessel — perhaps cast by a bell-founder who was used to working in such forms — with a large arrow projecting from its neck; a gunner is applying a taper to the touchhole and the device is aimed at a castle gate.
By the fifteenth century gun technology had advanced. Cannonballs had replaced arrows and the gun had assumed tubular form, sometimes achieved by binding billets of wrought iron, barrel-fashion, with iron hoops. Nevertheless, the use of the cannon remained confined to siege warfare. Though there were apparently cannon deployed at Agincourt (1415), they could as yet do little on the battlefield but make noise or smoke; it would have been an unlucky knight or archer who got in the way of a random shot. Forty years later, however, when the French finally expelled the English from Normandy and Aquitaine, in the campaign of 1450–3, they knocked through castle walls of the English strongholds with cannon; at exactly the same time the Turks were battering down the walls of Theodosius at Constantinople with monster bombards (the Turkish taste was for guns so large that they sometimes had to be cast in situ before a siege began). In 1477 Louis XI of France (1461–83) further extended his area of control over his ancestral lands by using cannon against the castles of the dukes of Burgundy. By 1478, as a result, the French royal house was fully in control of its own territory for the first time since Carolingian days six centuries earlier, and ready to erect a centralised government — supported by a fiscal system in which cannon were the ultimate tax-collectors from refractory vassals — that shortly became the most powerful in Europe.4
The cannon with which the French kings and the Ottoman Turks knocked through their enemies’ defensive walls suffered, however, from defects that gravely limited their military usefulness: they were large, heavy and mounted on immobile platforms. As a result they could be brought into action only on territory their owners already controlled, as the French did the Norman countryside and the Ottomans the water and land approaches to Constantinople. For cannon to become instruments of campaign they had to be lightened enough to be transported on wheels at the same speed as the army that accompanied them, so that foot, horse and guns could move as an integrated unit within enemy territory, thus averting the dangers that the artillery might be captured while gunners struggled to keep up with the marching force or have to be abandoned in the event of a retreat.
In 1494 the French achieved the appropriate breakthrough:
French craftsmen and bell-founders … by the [early] 1490s … had evolved a cannon that was recognisably the same creature that was going to decide battles and sieges for nearly four hundred years to come. The heavy ‘built-up’ bombard, firing a stone ball from a wooden platform that had laboriously to be lifted onto a cart whenever it changed position, had been replaced by a slender, homogeneous bronze-cast tube, no more than eight feet long, its proportions carefully calculated to absorb the progressively diminishing shock of discharge from breech to muzzle. It fired wrought iron balls, heavier than their stone equivalents but, because of that, of three times’ greater destructive effect for a given bore.5
Most important of all, the guns were mobile; because the tubes were cast in one piece, ‘trunnions’, short flanges projecting just forward of the point of balance, could be incorporated into them, by which they could be hung in wooden two-wheeled carriages. The cannon thus became as manoeuvrable as a small cart — even more manoeuvrable when the ‘trail’ of the carriage was hitched to another two-wheeled ‘limber’, forming an articulated unit to which horses could be directly harnessed between shafts; the carriage itself could be so fashioned as to allow the muzzle of the tube, or barrel (the nomenclature of the ‘built-up’ gun of hooped metal staves persists to this day), to be depressed or elevated by the manipulation of wedges under the breech. To traverse the gun from right to left or vice versa, the trail of the carriage, which rested on the ground to provide stability, was shifted in the appropriate direction.
In the spring of 1494, forty of Charles VIII’s new guns were shipped for him from France to the port of La Spezia, in northern Italy, whence, having brought his army across the Alps by the pass of Mont-Genèvre, he set off to march down the length of Italy to make good his claim to the kingdom of Naples. The city states and the papal lands that stood in his way gave up resistance as soon as they heard how quickly his guns had battered down the wall to the castle of Firizzano. In November he entered Florence as a conqueror. In February of the following year, having overwhelmed in eight hours the Neapolitan fortress of San Giovanni, which had once withstood a siege by traditional military means lasting seven years, he rode into Naples. The whole of Italy quaked at his passage. His guns had brought a true revolution in warmaking. The old high-walled castles against which both siege-engines and scaling-parties had so often failed were hopelessly vulnerable to the new battering-instrument. Guicciardini, an Italian contemporary, wrote that the cannon were ‘planted against the walls with such speed, the space between the shots was so brief, and the balls flew so speedily, and were driven with such force, that as much execution was inflicted in a few hours as used to be done in Italy over the same number of days’.6
Charles VIII’s Neapolitan triumph did not last. His barnstorming methods panicked the Italian states, Venice, the Holy Roman emperor, the Pope and Spain to form a league against him, and though his artillery gave him victory in the main battle of the ensuing War of the Holy League, Fornovo, he then decided to abandon Italy and return to France, where in 1498 he died. His artillery revolution, none the less, proved enduring. The new guns achieved an effect after which siege-engineers had striven for millennia without success. Hitherto the strength of a fortress had derived principally from the height of its walls. That was not exclusively the case, since water defences greatly enhanced defensibility also, as Alexander the Great found during the siege of the offshore stronghold of Tyre (332 BC), which took seven months to conclude. In general, however, the higher the wall the more difficult for the storming-party to scale the crest, while the thickness entailed by height rendered attack by siege-engines less effective. Opposed-weight engines (catapults) threw projectiles that struck only glancing blows at such walls, while torsion-machines, though working in a flat trajectory, were intrinsically underpowered. The only certain means of bringing a wall down was to attack it at its base by mining, a laborious task that ditches and moats readily defeated, and that was also open to the riposte of counter-mining.
The new cannon, because they could be brought rapidly into action close to a wall, and then handled to fire accurately in a predictable arc of impact, transferred the effect of mining to artillery. Iron cannonballs, directed at the base of a wall in a horizontal pattern of attack that did not vary in height, rapidly cut a channel in the stonework, the cumulative effect of which was to use the physics of the wall against itself: the higher the wall, the more quickly it would become unstable and the wider the breach it left when it toppled. Since in falling it automatically filled up the ditch at its foot with rubble, thus providing passage for an assault party, and probably brought down a tower as well (that would have been the artillerists’ intention, thus depriving the defenders of a dominating position from which to assail the assault party with missiles), the opening of the breach amounted to the fall of the fortress also; it was already a convention of siege warfare that a refusal to surrender after a breach had been made thereafter absolved the attackers from the obligation to offer quarter or abstain from looting. In the artillery age that convention became absolute.
The disasters in Naples naturally provoked a response. Existing castles were a first line of defence for many, particularly the smaller states of Renaissance Europe, their building and maintenance consuming a large part of state revenues, and fortification-engineers were put on their mettle by the ease with which Charles VIII’s cannon had knocked down walls that had stood stoutly for many centuries. In the wars between France, Spain, the Holy Roman empire and the shifting alliances of city states that troubled Italy in the first half of the sixteenth century, remarkable improvisatory works to strengthen old fortifications were achieved. At Pisa in 1500, for example, the city’s engineers contrived an inner earthen bank and ditch behind the city’s stone wall, which stood intact after the guns of the French and their Florentine allies had battered a breach. This ‘double Pisan rampart’ was much copied, while there was a great deal of building of external lines of earthen and timber walls and towers, against which iron cannonballs did little damage, at least in the early stages of a siege.7 City and fortress commanders also quickly recognised that breaches, once made, could be successfully defended by infantry equipped with firearms, effective models of which were just then coming into use, as their sharp practice at the sieges of Cremona in 1523 and Marseilles in 1524 demonstrated.
Improvisation, however, could not adapt old walls to withstand new cannon for ever. An alternative system of fortification was needed. The wonder is that it was found so quickly, so quickly indeed that the age of overwhelming artillery dominance was quite short, little more than a half-century. Measured against the pace of other adaptations to military innovation — that, for example, to armoured Blitzkrieg at the outset of the Second World War, which Hitler’s enemies contained by radical reorganisation of their armies and the mass manufacture of anti-tank weapons by 1943 — fifty years may seem a lengthy period. But that is to overlook both the intellectual difficulties and the costs involved. An anti-artillery concept had first to be thought out; then the funds had to be found to transform the concept into architectural reality — an enormous capital undertaking, since what was at issue was nothing less than the replacement of a continent-wide system of fortification built over many centuries (some towns sheltered behind walls that, though rebuilt and restored in the Middle Ages, were Roman in origin) of which the original costs had long been amortised.
Clever minds hit upon the germ of the concept almost from the moment mobile cannon appeared. Since cannons did their worst against high walls, new walls to resist them must therefore stand low. However, a fortress so built was open to escalade, the rush-forward of a storming-party with ladders to sweep over the crest and into the fortress’s interior by surprise attack. The new system of fortification had to incorporate features that resisted bombardment and, at the same time, held the enemy’s infantry at a distance. The solution to this problem of surrendering height while acquiring depth was the angular bastion, which stood forward of the walls, dominated the ditch or moat, served as a fire platform for both cannon and firearms, and was strong enough not to be battered shapeless by a concentration of enemy fire. The most suitable design proved to have four faces: two forming a wedge that pointed out toward the surrounding countryside so as to present a glancing surface to enemy fire, and where attacking artillery could be mounted, and two that joined the wedge to the wall at right-angles, from the rampart of which defenders could use cannon and firearms to sweep the ditch and stretches of wall between the bastions. The bastion should be built of stone, though brick was an acceptable substitute, backed and filled with rammed earth, the whole constituting a structure of immense solidity so as to provide both a solid cannon platform and an outer face on which impacting shot would make the least possible impression.8
Fortress-engineers had been experimenting with bastions, and had been thickening walls and sloping their faces, for some time before Charles VIII’s expedition into Italy in 1494 demonstrated that the castle had had its day. Such experiments had been scattered and piecemeal, but those who undertook them were thereby sufficiently attuned to the demand for innovation to respond with speed and energy. Giuliano da Sangallo, who with his brother Antonio founded the first and most important of a group of Italian fortification ‘families’, had drawn up a design for a bastioned defence of the town of Poggio Imperiale in 1487, while in 1494 itself Antonio had begun to reconstruct the fort of Civita Castellana on a bastion system for Pope Alexander VI.9 Convinced that such systems offered the answer to artillery attack, they were soon proceeding apace with new works for any Italian government that could find the necessary money; Nettuno was outfitted with bastions between 1501 and 1503, and in 1515 Antonio undertook to construct a model fortress for Cardinal Alessandro Farnese at Caprarole. The Sangallos’ commercial success attracted competitors into the field, first the San Micheli family, then the Savorgnano, Peruzzi, Genga and Antonelli.
The money to be made invited envy and drew all sorts of unlikely practitioners into the market, including both Leonardo da Vinci,10 who was inspector of fortresses for Cesare Borgia, and Michelangelo, who in the course of an argument with Antonio da Sangallo in 1545 announced, ‘I don’t know much about painting and sculpture, but I have gained great experience of fortifications, and I have already proved that I know more about them than the whole tribe of the Sangallos.’11 Michelangelo equipped his native Florence with new defences between 1527 and 1529 but, fortunately for art, thereafter found fewer commissions for his fortification skills.
The Sangallos and other fortification families were kept in almost continuous employment, not only in Italy but, as their fame spread and rulers acquired ever larger numbers of mobile cannon, in France, Spain, Portugal, the Aegean, Malta (where the Hospitaller order had settled after its expulsion from the Holy Land) and as far away as Russia, West Africa and the Caribbean. They, with the artillerists whose weapons confronted them with their challenge, were the first international technical mercenaries since the builders of chariots who had sold their skills to the warring aristocracies of the Middle East during the first millennium BC. An Italian historian has described their way of life:
We must put ourselves in the position of these men. They were short of money, and yet they were aware of their own talents and regarded themselves as superior beings who moved among folk who were less civilised than the Italians. They were upset by the example of the few men among them who rose to the highest ranks, and they were liable to go off and serve the most distant prince who attracted them by tempting promises. And yet they did not end up any better off — their creditors were many, their purses light and the expense of long journeys made it difficult for them to return to their homelands. They had to put up with the scorn which the soldiers reserved for those among their comrades who tried to combine the theory of war with the weapons of war.12
If fighting soldiers, many of them also mercenaries themselves, scorned the engineers, it was for reasons of warrior pride, not because the new fortifications failed in the purposes for which they were erected, at such enormous cost and labour. The reality was quite the contrary: the bastion fortress restored the advantage of defence over offence as rapidly as cannon had reversed it at the end of the fifteenth century. By the end of the sixteenth, the frontiers of every state that aspired to preserve its sovereignty were protected at the most vulnerable points — mountain passes, river-crossings, navigable estuaries — by modern defences. The internal pattern of fortification was also altered: there were few ‘star’ forts’ in the hinterland, for kings used their monopoly of expensive artillery to push over the strongholds of their last dissident grandees and to prevent them rebuilding castles with bastions. At the frontiers, however, fortification was becoming denser than it had ever been before, and much more effective as a means both of imposing a military barrier and of defining the outlines of a government’s jurisdiction. The modern frontiers of Europe are, indeed, largely the outcome of fortress-building, by which existing linguistic and the new, post-Reformation religious boundaries were teased and chivvied into neatness.
Nowhere was this more evident than in the Netherlands where ‘above the rivers’, the Rhine, Meuse and Scheldt, which flow together into the North Sea, the Protestant Dutch subjects of the Catholic Spanish kings (Habsburgs after 1519, who in their persons united the imperial lands of Austria, Germany and Italy as well) raised rebellion in 1566. The war, which lasted eighty years, merged with the Thirty Years’ War in Germany (1618–48) and spawned such subsidiary conflicts as the campaign of the Spanish Armada against England in 1588. The Dutch were able to sustain resistance for so long for two reasons: through their access to the sea and control of the river routes upstream into central Europe they were already becoming a trading nation soon to equal Venice in wealth; and their wealth permitted them to build the fortresses that enabled them to assert their independence. The secretary to the Spanish governor, Requesens, reported in 1573 that ‘the quantity of rebel towns and districts is so great that they embrace almost all of Holland and Zeeland, which are islands that can be reduced only with great difficulty or by naval forces. Indeed, if several towns decide to hold out, we shall never be able to take them.’13 Such towns did so decide, their populations throwing up earthen bastion fortifications where stone or brick did not yet stand. Even a few such fortified places sufficed to hold the Spaniards at bay; the towns of Alkmaar and Haarlem were so strongly defended that they consumed the military effort of the whole Spanish counter-offensive in 1573.
Siege warfare was time-consuming and laborious because the means of bringing sufficient fire to bear against a bastion fortress demanded an enormous effort in excavation. The bastion fortress was a ‘scientific’ construction, which meant that its design was arrived at by mathematical calculation of how best to minimise the wall area that shot could strike and to maximise the area of open ground outside it that defending fire could sweep. The attack had therefore to be ‘scientific’ also. Siege-engineers soon worked out the principles. A trench had to be dug parallel to one side of a bastion trace, in which guns could be sheltered while they began the bombardment. Under cover of that fire, ‘approach’ trenches were then pushed forward until another ‘parallel’ could be dug closer in, to which the guns would be brought up to continue the bombardment at closer range. It was eventually found — Vauban, Louis XIV’s master siege-engineer, perfected the technique in the seventeenth century — that three parallels was the necessary number to dig; from the last, sufficient weight of fire could be mounted to batter a bastion into rubble, fill the ditch with the detritus and so give the infantry massed in the last parallel the fighting chance of rushing the breach.
Infantry assault on a bastion fortress, however badly it had been knocked about, nevertheless remained always a desperate business; it was a universal defensive practice to keep handy the materials — cylindrical baskets to contain earth, called gabions, posts, rails and wooden barricades — with which an inner defence could be improvised behind a breach, while musketeers and gunners from an adjoining bastion could always direct withering fire on any assault party that crossed the ditch or even reached the sloping ‘glacis’ outside it. The horrors of the assault did not, however, constitute the sixteenth-century infantryman’s principal objection to siege warfare. What he objected to was the labour of digging, particularly in Holland, where the water table might be struck two feet below the surface. Parma, one of the principal Spanish commanders, resorted to paying diggers extra — the practice was to become almost universal in the next few centuries — but he still ‘had to do battle with the twisted pride of the Castilians, who regarded begging in the streets as more honourable than labouring for a reward’.14
The Spaniards nevertheless made progress during the first twenty years of the Dutch revolt, subduing the rebel towns between the Scheldt and the Meuse in what would later become northern — and Catholic — Belgium. Into the even more waterlogged country north of the Rhine and west of the Ijssel, which contained the great cities of Rotterdam, Amsterdam and Utrecht, Spain could make no progress. By 1590 the commanding general of the Dutch armies, Count Maurice of Nassau, who, with his cousins William Louis and John, was to reintroduce from classical literary models the discipline and drill of the Roman legions, had assembled sufficient force to go over to the offensive. Between 1590 and 1601 he pushed the Dutch frontier south of the Rhine, so securing such places as Breda in perpetuity for Holland and ensuring that Eindhoven would eventually fall also; meanwhile he was also reducing the Spanish garrisons in the northern Netherlands, thus clearing the way for the future kingdom of Holland to have a frontier solidly abutting against the German-speaking lands. In 1601 the Spanish caught Maurice out when he ventured beyond ‘Fortress Holland’ toward Ostend, a fortified Dutch outpost which they eventually took at the end of a three-year siege; however, they so exhausted themselves, financially rather than militarily, in the ensuing campaign that by 1608 they were ready to agree to a truce. It did not last the specified twelve years. By 1618 a larger war had broken out in northern Europe, the Thirty Years’ War, in which gunpowder put the participants to a far more gruelling test than the static fortress battles between Dutch and Spanish had ever done.