Philip the Bold, duke of Burgundy, was a warrior’s warrior. Hawk-nosed, ambitious, and brash, Philip had been a soldier since childhood. He was still a smooth-faced boy of 14 when he fought alongside his father, King John II of France, in the battle of Poitiers in 1356. Like King John, he was taken prisoner by the English when Edward, the Black Prince of Wales, vanquished the French on the field at Poitiers. A decade later, the duke, always looking for an advantage over the Englishmen who had invaded his country, embraced a novel technology: gunpowder.

This mysterious Asian invention had been known in Europe for more than a century, and for nearly that long European armies had used it as a weapon of war—or, more precisely, as the substance that made another recent innovation, the cannon, work. So far, gunpowder artillery had not shown great promise. Cannon had been used as siege engines in European warfare at least as early as the 1320s. But for all the trouble and effort they demanded, they had not proven themselves to be much more effective than conventional siege weapons such as catapults and trebuchets, machines that used mechanical energy to hurl projectiles at castle walls. Certainly, the early cannon did not appear to be effective enough to justify their cost, which was substantial.

But Philip the Bold saw promise in the new weapons, especially the huge siege guns that came to be known as bombards, and in 1369 he began to invest heavily in them. France and England were then locked in the on-again, off-again series of dynastic conflicts known today as the Hundred Years’ War (1337–1453). In 1377, when Duke Philip’s brother and sovereign, King Charles V of France, ordered him to attack the English in the Calais region, the duke answered the call, bringing with him more than 100 new cannon, including one monster of a gun that fired a stone cannonball weighing some 450 livres (around 485 pounds).

One of the duke’s intended targets was the English-held castle at Odruik, built with stout masonry walls and surrounded by a thick layer of outworks. Odruik would be a tough nut to crack. Its defenders seemed to think so, too, and were confident that they could hold out against Duke Philip’s army, even as the duke’s men began to put their huge siege cannon into position in full view of the castle walls.

The first few shots from Philip’s siege-battery hammered Odruik’s outer walls into dust. Soon, the stone cannonballs were sailing through the walls as if they weren’t there; soon after that, the outer walls actually weren’t there. After Philip’s guns had fired a grand total of about 200 rounds, much of Odruik’s once-proud walls lay in ruin, and before the duke could send his men through the breach and into the castle, Odruik’s defenders capitulated.

Philip the Bold’s triumph at Odruik in 1377 was a harbinger of things to come, a revealer of unsettling truths. Gunpowder artillery had been used in sieges before, but Odruik was its first overwhelming and clear-cut victory over a castle. The siege of Odruik demonstrated that—when the guns were big enough, and when there were enough of them—cannon were more powerful than any siege engine yet invented, and could knock down castles in a matter of hours. What happened at Odruik would be repeated over and over again at castles throughout continental Europe and the British Isles through the remainder of the Middle Ages and beyond.

Over the century to come, gunpowder began to leave its mark on the conduct of war in the West; access to superior siege artillery would make the difference between victory and defeat in land warfare. With artillery, the French would drive the English from their soil in the closing phases of the Hundred Years’ War, turning defeat into triumph. With artillery, Christians in Iberia would drive the Moors from their last strongholds in Granada, ultimately creating Europe’s first superpower: Spain. And in 1453, the Ottomans, also avid students of gunpowder artillery, would use their massive bombards to break down the walls of ancient Constantinople and destroy the last vestiges of the Roman Empire.

After Odruik, artillery would spell both the end of the castle and the emergence of a new kind of warfare, based on firepower, that relied on the massed use of gunpowder weapons for siege, on the battlefield, and at sea. Within a century and a half of Philip the Bold’s quick and noisy victory, very little about European warfare would even vaguely resemble what had come before. The weapons, the size and organization of armies, the role of fighting men and leaders—even the sounds, the smells, and the scale of the European battlefield—would be radically transformed by the advent of gunpowder weaponry. And the implications for life beyond the narrow horizons of the battlefield were even more profound.

Artillery meant the end of the castle, an edifice that both symbolized the independence and power of local warlords in medieval Europe and gave those warlords a means of resisting the encroaching ambitions of central governments embodied in Europe’s emerging dynastic monarchies. The cannon took down the autonomy of the old warrior aristocracy just as it did the walls of their castles; the onerous expense of making and maintaining cannon meant that only the wealthiest lords—the monarchs themselves—could afford to build up their arsenals of these terrifying new weapons. The cannon, in short, concentrated military force and political authority in the hands of the state at the expense of noble warlords.

What made artillery possible was gunpowder, and gunpowder was the single greatest invention of the European Middle Ages, even if it wasn’t actually European. It was first developed in China as early as the ninth century AD, and over the intervening centuries the Chinese had become proficient in its use. They employed the substance as an incendiary at first, only later discovering that it could also be used as an explosive and as a propellant, two related but distinctly different roles.

Just when gunpowder first came to Europe, and how it did so, remain mysteries. It may be that the Mongols, who used gunpowder weapons, unwittingly passed it along during one of their incursions into Europe’s eastern borderlands in the 13th century.

The English scholar Roger Bacon mentioned gunpowder in his treatises Opus Majus and Opus Tertium (ca. 1267); a German cleric named Berthold Schwarz, likely mythical, has sometimes been given credit for conducting early experiments with the substance. In the end, it matters little. Like most debates over “who did what first” in history, disputes over the origins of gunpowder ultimately settle nothing. Suffice to say, the Chinese invented gunpowder and pioneered its use; in some fashion, Europeans acquired it from the East, and their use of it developed independently of Asia.

From the time of its first use in the Middle Ages until its replacement by better propellants and explosives in the 19th century, gunpowder went through a continual process of reinvention and reformulation. Its basic composition, however, remained the same throughout: roughly 75 percent saltpeter (potassium nitrate), 15 percent softwood charcoal, and 10 percent sulfur, by weight.

Gunpowder, also known as black powder, is neither an ideal explosive nor an ideal propellant, and its salient properties are unlikely to inspire much confidence. As originally formulated, black powder was a simple mixture, produced by combining the three ingredients with mortar and pestle. The substance is volatile, easily ignited by spark or flame. But it is just as easily rendered neutral: water, even excess humidity, can make it useless.

Gunpowder doesn’t actually explode when ignited. Rather it deflagrates—it burns rapidly—which means that it is better suited to its propellant role than to its role as an explosive. Black powder burns much faster than modern smokeless powders, and when used as a propellant with a projectile, it produces lower velocities than modern, slower-burning powders do.

Black powder also burns inefficiently, creating two byproducts when ignited, both of them undesirable: smoke and fouling. Burning black powder produces clouds of acrid white smoke, enough to give away the position of a shooter with a single shot, enough to obscure visibility when fired from many weapons or from larger weapons. After combustion, black powder leaves behind hard carbon soot. In firearms, this residue—called fouling—can have serious consequences. Prolonged firing of black powder in a gun barrel will result in the deposit of layer after layer of fouling, gradually constricting the interior of the barrel (the bore), making the task of loading difficult or even impossible.

Gunpowder may not have been an ideal propellant or explosive, but in 1400 it had no competitors, and for all its faults it was effective enough. It would not have to wait very long for a military application.

That application was the practice of siege warfare. No form of land-based combat has been more commonplace than the siege, throughout the sweep of human history from the earliest known wars to the investment of Leningrad in 1941–1944. Pitched battles between armies or navies attract more attention, for they are suited to storytelling: battles are concise, they have movement instead of stasis, they have a narrative arc—battles are the stuff from which high drama is wrought. Yet the siege, for all its mechanical drudgery, is universal. Before the 20th century, the siege was the principal kind of hostile interaction between opposing armies, and was far more common than the pitched battle. Sieges were also costlier, consuming more resources—men, materiel, and time—than pitched battles.

In the Middle Ages, the principal locus of the siege was the castle. Castles made their first appearance in Europe in the ninth century, rising up amid the fragmented remains of Charlemagne’s empire. As the fortified residences of powerful lords, castles would become closely linked to, and emblematic of, the feudal system around which so much of Western European social and political life revolved. Castles functioned as seats of local authority and justice, a means of controlling and protecting the villages that sprang to life around them. They could serve, also, as focal points for rebellion. For a willful vassal who did not feel inclined to obey his lord or king, a castle was a sanctuary and a power base. In the emerging kingdoms of the High Middle Ages, castles strengthened the power of the noble landowning class, often at the expense of royal power.

Castles, in short, had a significance that went far beyond their military function, but first and foremost they were fortifications. In the Holy Land, the great castles of the Crusaders—such as the imposing Krak des Chevaliers in Syria—allowed European invaders to maintain a near constant presence in the region, to defend the fragile Crusader states, and to mount offensive operations. English military operations in France during the Hundred Years’ War revolved around the construction and possession of castles. As with any technology whose useful life spans centuries, the design of the castle was constantly evolving. The motte-and-bailey fortifications of the 10th century would seem puny and impotent when compared to the stone-built castles of the 13th.

From a military standpoint, the castle proved to be such an enduring technology because it was good at fulfilling its main purpose: to keep hostile forces out, and to keep the people within safe. High walls and fortified gates guarded against forced entry; masonry walls were impervious to flame; and towers with loopholes—thin vertical firing slits for archers—gave a modicum of protection, making it potentially costly for a besieging army to move close. So long as the defenders were adequately provisioned and had ready access to water, a castle could hold out indefinitely. For a besieging army, if a castle could not be taken by storm, or its garrison intimidated or starved into capitulation, then it would have to be reduced.

Reducing a castle was an uncomplicated process, and quite literally mechanical, in the sense that it involved the use of machines or siege engines. While it was possible to bring down an outer wall by sapping—that is, by tunneling under the very foundations of the castle, causing the walls to sink and hopefully to collapse—breaching a wall by means of siege engines was the preferred method. Medieval siege engines, or “mechanical artillery,” had changed little since late antiquity: a mechanical force—torsion in catapults, counterweights in trebuchets, and human brawn in onagers—powered a heavy throwing arm that could hurl a heavy projectile, like a large stone, and send it crashing against the castle’s outer walls. Though simple in concept, the act of smashing walls with such weapons was laborious and time-consuming. It could be costly in lives, too, if the crews operating the machines were exposed to archery, which was likely because the range of catapults and trebuchets was quite short. A heavy trebuchet could not toss a large stone much further than 200 yards, within effective longbow range. Consequently, the results were often long in coming.

This is where gunpowder came in, but not as an explosive— which, perhaps surprisingly, was almost an afterthought. It wasn’t until late in the 15th century that European soldiers began to use gunpowder in so-called mines: massive quantities of gunpowder packed in tunnels dug beneath the castle walls. When detonated, such subterranean mines could collapse the sturdiest wall in moments. Instead, gunpowder found its first serious employment as a propellant in a primitive gun. That technology—compressing a charge of gunpowder in a tube that was closed at one end and open at the other, so that the expanding gases from the deflagrating powder would push out a projectile with great force and speed—was also a Chinese invention. In Europe, when gunpowder arrived, the knowledge of primitive firearms arrived with it.

The first major use of firearms in the West involved truly big guns, what we know as gunpowder artillery. That might appear counterintuitive. Small, logically, should precede big. But small arms, handheld firearms, were later additions to the European arsenal. The first functional firearms in the West were cannon.

A cannon, or bombard, might seem like the simplest of weapons, but in the Middle Ages metallurgy and metalworking had not yet advanced to the point where it was possible to cast a large tube in one piece, at least not in any metal sturdy enough to withstand the shock released by the deflagrating gunpowder. The first cannon were of “hoop-and-stave” construction, products of the cooper’s art rather than the iron-founder’s. Long wooden staves were laid together in parallel around a central core, and were then bound together and reinforced by hoops of wrought iron. Soon iron bars replaced the wooden staves. The resulting tube was open at both ends, and so the first European cannon were breechloaders—the powder and projectile were loaded not from the muzzle, where the projectile exits the barrel, but from the opposite end. A separate breech-piece acted as a powder chamber; it was attached to the open breech-end of the tube, and was then secured in place with a wooden wedge.

There was not much about such a weapon to inspire confidence. Even ignoring the many serious deficiencies of gunpowder, the cannon themselves had plenty of problems of their own. Hoop-and-stave construction is inherently weak. The earliest pieces burst frequently, and were nearly as dangerous to their gun crews as they were to their intended targets. And because it was impossible to create an airtight seal between the open-ended tube and the breech-piece, there would always be a gap between the two. Hot gases would leak from the gap when the gun was fired, bleeding off some of the energy of the deflagrating powder and potentially burning anyone unwise enough to stand close to the gun.

These early gunpowder monsters were crude weapons, to be sure, and their performance reflected it. In all the ways that we assess firearms—range, accuracy, rate of fire, reliability—the bombards came up short. But in the 14th century, there was simply nothing better to which they could be compared. Their range was limited, but they needed only to outrange an arrow or a crossbow bolt so that their crews could work safely outside arrow range. Their accuracy was poor, but their targets were anything but small; they needed only to be able to hit the towering outer walls of a castle. Their projectiles flew slowly, but they only needed enough force to shatter brick or stone masonry. They were slow to load and fire, but siegecraft demanded patience, not speed.

In short, to justify its existence and the not-inconsiderable sums of cash and materials that it consumed, gunpowder artillery only had to be better and faster at smashing castle walls than the catapult and the trebuchet. Even in its earliest, crudest, most primitive forms, the bombard met those criteria. Besides, the catapult and the trebuchet were the late-generation offspring of a venerable, mature technology, at the apex of their potential, unlikely to be improved upon. Gunpowder was yet in its infancy. There was nowhere for it to go but up.

And up it went. Between the mid-1300s and the early 1500s, gunpowder artillery advanced rapidly, or as rapidly as any technology would before the modern era. During this period, cannon would assume most of the characteristic features that would carry the weapon through to the 19th century. Advances in metallurgy and the metal-founder’s craft account for most of those advances. European artisans learned to cast cannon out of iron and bronze—solid, in one piece, much as church bells were cast. Bronze, an alloy of copper and tin, was the preferred material; cast bronze wore better and longer than cast iron, and cast-bronze cannon were thought to be less prone to bursting when fired. Cast iron, on the other hand, was cheaper and slightly less dense. The two materials would predominate in artillery manufacture until the advent of mass-produced steel, later in the 19th century.

The greater expense of cast-metal cannon tubes was worth the investment. They were infinitely more stable than the early hoop-and-stave guns. That was a great advantage in itself, but there was more to it. Solid-cast cannon had to be loaded from the muzzle, since the cast gun would by definition be closed at the breech-end. Powder and projectile would have to be inserted from the muzzle and then rammed down the length of the bore. A narrow vent, drilled through the breech into the bore, allowed access to the main powder charge after it was loaded, so that it could be ignited from the outside of the barrel via a priming charge inserted into the vent. To modern eyes, this transition—from breech-loading, a common feature of nearly all modern firearms, to muzzle-loading, which seems quaint and old-fashioned—appears retrograde. But it was actually a great leap forward. A cast, muzzle-loading cannon does not leak gas at the breech. The inherent strength of its construction meant that it could tolerate heavier charges, heavier projectiles, and more powerful powders without bursting.

That added strength came in handy, for gunpowder too was evolving. The constituent elements and their proportions would remain essentially the same for a long time, but the method of processing the ingredients was becoming more sophisticated. The original formulation of gunpowder, popularly known as serpentine, was compounded dry, the ingredients ground together to make a fine dust. When jostled in transport, the charcoal, saltpeter, and sulfur tended to separate, so the gunpowder would have to be reblended before use. That was a tricky and hazardous chore, one best left to an experienced gunner.

At the end of the Middle Ages, though, European powder makers had stumbled upon the process of corning. Corned powder was made by moistening the mixed serpentine, usually with water, sometimes with other liquids; artisans passionately debated the relative virtues of wine and urine for corning. The dampened powder was pressed into cakes, allowed to dry thoroughly, and then milled into “grains” or “corns.” Corned powder didn’t separate, didn’t have to be reblended before use, and gunners found that it burned more efficiently and predictably than serpentine. Soon powder makers were producing specialty powders: slower-burning, coarse-grained powder for artillery, finer powders for small arms, the finest powder for priming. Gunners discovered, too, that the corned powder was more powerful, and for that cast guns were perfectly suited. Hoop-and-stave guns were nowhere near sufficiently robust to handle the new formulations, and they began to fade away.

Cannon tubes cannot stand on their own. They require a carriage or mount, for transportation and for aiming. The earliest mounts were simple wooden beds to which the gun tube could be strapped. Wheeled gun carriages, which first appeared in Europe early in the 16th century, were far more mobile, and made the process of aiming simpler and more precise. When combined with a new design feature called the trunnion—a pair of solid metal cylinders projecting from the sides of the cannon barrel just forward of the tube’s center of gravity, cast integral with the barrel—the wheeled carriage was nothing short of revolutionary. Trunnions held the gun more securely to the carriage, and—most important—they made it so the gun could be elevated or depressed, tilting the muzzle up or down so as to increase (or decrease) the gun’s range. Ultimately, the wheeled carriage would make possible the first truly mobile field artillery, cannon that could be used on the battlefield alongside infantry and cavalry, and deployed as necessary. That day, though, was still some ways off. For now, cannon were too bulky to play an important role outside of the siege.

Artillery ammunition was simple. The most common form at the time of the Renaissance was the solid shot, a simple sphere, which in the early days of gunpowder artillery was usually made of chipped stone. Stone balls had a few advantages over cast-iron: they could be produced on-site during a siege, for instance, and they were typically lighter than cast-iron balls of the same size. Cast-iron shot, on the other hand, tended to hit harder and travel farther than stone, but their greater weight required a heavier powder charge and therefore were more stressful on gun barrels. But once cast-metal guns became available, the cast-iron solid shot caught on.

What made iron shot practical was an innovative and novel concept: standardization. Here, history has given the lion’s share of the credit to a remarkable team of brothers, Jean and Gaspard Bureau. The Bureau brothers were not soldiers so much as they were professional artillerists, and until the 18th century European artillerists considered themselves members of an elite, highly technical craft guild rather than military men. The Bureau brothers, as manufacturers and professional gunners, understood cannon inside and out. During the last two decades of the Hundred Years’ War, they served as commanders of the French artillery train.

Their king, Charles VII (r. 1422–1461) of France, trusted the Bureau brothers and allowed them much latitude, and the brothers put that trust to good use. They encouraged gun-founders to use cast iron instead of the more expensive cast bronze, and they promoted cast-iron shot over stone. By far their greatest achievement was the reduction in the number of types of cannon to a few standard models. In the 15th century, long before manufacturing introduced the notions of interchangeable parts and precision measurement, standardization was a pretty loose concept. Cannon were still individually crafted, as everything was.

Rather than leave the dimensions of cannon tubes up to the gun-founders, as had been the practice before, the Bureaus set rough universal measurements to which all makers had to adhere. Guns of a particular class would all be roughly the same length and the same weight, of the same materials, and use the same carriage. More important, they would all have the same bore diameter, which meant that they could all fire the same shot.

Excerpted, with permission, from Firepower: How Weapons Shaped Warfare, by Paul Lockhart. Copyright © 2021 by Paul D. Lockhart. Published by Hachette Book Group Inc.