27 Siege Machines in the Crusades

Introduction: weaponry in the name of religion

The Crusades, a series of religious wars between Christian and Muslim forces from the 11th to 13th centuries, were defined not just by spiritual conflict but by technological innovation. These battles were fueled by both religious motivations and geopolitical aspirations, leading to some of the most prolonged and intense military campaigns in medieval history. The siege of Jerusalem in 1099, for example, highlighted the importance of siege warfare as Crusaders used ladders, battering rams, and mangonels to breach the city’s defenses. Success in such sieges was often pivotal: capturing fortified cities like Antioch or Jerusalem could decisively shift the balance of power. These wars ushered in an era where the effectiveness of an army was increasingly linked to its mastery of engineering and siegecraft. Siege machines became vital instruments of conquest and survival, enabling armies to penetrate fortifications that symbolized political and spiritual power. As historian Mark Cartwright (2018) explains, siege warfare in medieval Europe eventually became more frequent than open battles, necessitating significant strategic, technological, and societal adaptations. The Crusaders and their Muslim counterparts quickly realized that faith alone would not decide these contests; technological prowess and innovation on the battlefield were just as critical. This dynamic set the stage for a dramatic interplay between religious fervor and mechanical ingenuity, as each side raced to out-engineer the other in the name of victory and divine favor.

Siege warfare & sts: a symbiotic evolution

The evolution of siege technology during the Crusades reveals a deep interconnection between science, technology, and society (STS). The pressing need to overcome complex fortifications drove the development of increasingly sophisticated weapons—from trebuchets and mangonels to siege towers and battering rams. Engineers and craftsmen applied principles of physics and mechanics (such as leverage, torsion, and gravity) to build machines capable of toppling castle walls. These machines incorporated concepts of force, counterbalance, and tension that reflected a growing practical understanding of engineering in warfare. For instance, historical analysis shows that Crusaders employed not only traction trebuchets (powered by manpower pulling ropes) but possibly torsion-powered catapults as well, which used twisted ropes or sinew for power​. This finding suggests that technology from the classical world (like the torsion catapults of Rome) may have seen continued or earlier-than-expected use in the First Crusade, illustrating how scientific knowledge was repurposed to meet new battlefield challenges. Likewise, by the 12th century the introduction of the counterweight trebuchet – a gravity-powered engine swinging a weighted arm – marked a significant leap in siege engineering. Such advances did not happen in isolation; they were often the result of cultural exchange. Crusaders learned from and collaborated with allies (such as Byzantine Greeks) and even observed techniques from their adversaries. In fact, medieval accounts indicate that the Franks and their Muslim foes learned from one another how best to create and use siege artillery, sharing ideas in a land where resources like wood were limited​.

The production and deployment of siege machines required massive human and material resources, linking technology to social organization. Armies on campaign became moving workshops: artisans, carpenters, blacksmiths, and engineers traveled with the Crusader host, applying scientific principles in real time to solve battlefield problems. Building a trebuchet or a siege tower was not trivial—it demanded precise calculations, quality materials, and skilled labor. The materials and labor invested illustrate the social and economic commitment behind these military campaigns. Timber had to be felled or procured, ropes woven, metal fittings forged, and thousands of man-hours expended in construction. The logistics of moving and supplying a medieval army often determined what siege technologies could be built on site. In the resource-scarce landscapes of the Levant, this meant innovation was necessary. Siege engines were commonly assembled from local timber upon arrival and could be disassembled afterward if time permitted​. In some cases, strategists began prefabricating components of siege engines in anticipation of campaigns – an early form of modular design – so that machines could be more quickly rebuilt at the next site​. This practice, noted by historians, emerged as sieges became more frequent and wood grew scarce in certain regions, forcing a shift in how technology was managed logistically. The willingness of medieval societies to mobilize resources and adapt techniques underscores a symbiotic evolution: societal needs spurred technological innovation, and those innovations in turn reshaped how society organized for war. European forces, driven by religious zeal and territorial ambition, adapted their engineering strategies to the battlefield—proving that faith and science could coexist, even in war. Indeed, the development and transport of siege engines during the Crusades showcased advances in project management and logistics long before those concepts were formally recognized. It was an age when the moral purpose of a holy war went hand in hand with practical problem-solving: the result was an unprecedented flowering of military engineering underwritten by social cooperation and inspired by necessity.

the function & form of siege machines

Siege machines served specific and critical purposes during Crusader assaults, and their forms followed their functions. Trebuchets and mangonels were designed to hurl projectiles over or against defensive walls, using either counterweights or twisted rope tension to generate force. These stone-throwers could launch massive rocks to smash ramparts or rain down death from above. In practice, the goal was not always to breach walls directly; often, commanders aimed to loft missiles over the battlements to strike defenders and sow chaos inside the fortifications​. Chroniclers recount that during protracted sieges, attackers sometimes hurled not only stones but also diseased animal carcasses or even human remains into cities, hoping to spread fear and disease — an early form of biological warfare and psychological intimidation​. The counterweight trebuchet, which came into wider use in the 12th and 13th centuries, was especially feared. This engine’s design featured a long wooden arm with a heavy counterweight on the short end and a sling on the long end. When the counterweight dropped, it propelled the sling upward, flinging its payload with tremendous force. A well-constructed trebuchet of the Crusades era could reportedly throw a 100–200 pound stone roughly 80–100 yards (up to about 75 meters)​, enough to batter walls or hit targets deep inside a courtyard. Some accounts suggest the Crusaders learned of this powerful design from their adversaries: it appears the concept of the counterweight trebuchet (an improvement on earlier designs that relied on manpower or torsion) was transmitted from the Muslim world to the Europeans during this period​. In earlier siege engines, like the Roman-era onagers, energy was provided by twisted cord or sinew; by the time of the later Crusades, gravity and counterweights had taken precedence, demonstrating a clear technological evolution that likely resulted from cross-cultural exchange.

Battering rams were another indispensable tool, built to break through gates or weak points in a wall’s construction. A typical battering ram consisted of a large heavy log, often capped with an iron head, suspended by ropes or chains within a mobile shed. The shed (sometimes called a tortoise or cat) was usually a wooden frame with a roof, frequently covered in wet hides to protect the crew from fire. Under this shelter, soldiers would swing the ram repeatedly to smash masonry or crack timbers. Such rams were crucial for assaulting fortified city gates, which were usually among the strongest points of a castle or town’s defenses. Siege towers, essentially mobile wooden towers sometimes several stories high, were engineered to solve the problem of scaling high walls. These massive structures were rolled up to the fortifications to allow attackers to climb over the top of enemy walls under cover. Inside, they contained ladders or ramps, and on top a drawbridge that could be dropped onto the parapet. Building a siege tower required an enormous quantity of timber and careful design to ensure it was tall enough to equal or exceed the height of the walls. During the First Crusade’s Siege of Jerusalem (1099), for example, the Crusaders famously constructed two immense siege towers. Lacking wood in the surrounding area (the defenders had stripped the countryside bare), the Crusaders were saved by the timely arrival of Genoese and English ships at Jaffa bearing ready timber and rope​. Using these supplies, they assembled the towers and other siege machines on site, dramatically improving their odds of success. Indeed, contemporaries noted that without this material support the capture of Jerusalem might have failed. This episode underscores how tightly function and form were wedded to available resources: the very design of a siege engine (its size, materials, and feasibility) was constrained by what an army could source or supply in a given theater of war.

Each type of siege machine reflected a balance between destructive power, cost, and practical construction, requiring both skilled labor and careful planning to deploy effectively. Trebuchets and other artillery could terrorize and demoralize as much as kill; the sight of a giant throwing engine being assembled outside one’s walls often sent a psychological message of impending doom. The mere visibility and scale of these machines signaled an overwhelming assault that could weaken the defenders’ resolve before any blow was struck. Defenders, for their part, devised counters: they might launch sorties to burn the wooden engines, use archers and crossbowmen to harass siege crews, or hang padded covers on walls to cushion impacts. To answer the battering ram, they dropped heavy stones or poured incendiary Greek fire onto the ram’s shed (Greek fire, a flammable compound of naphtha, pitch, sulfur and other ingredients, could stick to targets and burn intensely​). In one recorded instance during the siege of Jerusalem, the defenders hurled burning bundles of straw and wood dipped in oil over the walls to set the Crusaders’ siege towers alight​. The attackers responded by quickly dousing flames and pressing on with relentless determination. This cat-and-mouse interplay meant that siege warfare was as much about engineering resilience and improvisation as it was about offense. Notably, siege warfare also drove defensive innovation: as siege engines grew in power, castle and city architects in turn reinforced and reimagined fortifications. Walls were built thicker and higher, towers were made rounder (to better deflect stones), and gatehouses became deadlier choke points. The function and form of each new siege machine thus directly influenced the evolution of military architecture, creating an arms race between the attacker’s technology and the defender’s design​. By the end of the Crusading era, the art of siegecraft had reached a high medieval peak — soon to be rendered obsolete by the advent of gunpowder, but forever a testament to human ingenuity in the pursuit of both destruction and survival.

Cultural impact & the crusades’ broader consequences

The significance of siege warfare in the Crusades extended beyond the immediate battlefield, leaving lasting cultural and technological ripples. As Cartwright (2018) notes, the Crusades influenced not only the course of wars but also the development of European monarchies, the military orders, and long-term East–West relations. Victories in major sieges often translated into territorial control, political authority, and even religious validation: a successful siege could be portrayed as a sign that God favored the victors. For example, the capture of Jerusalem in 1099 – achieved through siege machinery and grim determination – was heralded in Europe as a miraculous triumph, bolstering the prestige of the Crusader leaders and inspiring further crusading efforts. Conversely, the failure of a siege could deal a devastating blow to morale and reputations. The disastrous attempt to besiege Damascus during the Second Crusade (1148) not only ended in retreat but also shook the confidence of Christendom and tarnished the aura of invincibility that the Crusaders tried to cultivate. In this way, the outcomes of siege warfare had societal consequences: they could ignite religious fervor or fuel despair, strengthen a leader’s legitimacy or precipitate their downfall.

Beyond immediate morale, the Crusades prompted a two-way exchange of military knowledge between East and West. Siege techniques and technologies did not remain proprietary to one side; each learned from the other. Western Crusaders, initially less experienced in protracted siege operations, adapted quickly by observing Byzantine and Islamic methods. They learned to incorporate advanced torsion artillery and incendiary weapons, while Muslim forces, in turn, adopted or improved upon European methods such as counterweight siege engines – heavy artillery that some Muslim chroniclers had not seen before the Crusaders arrived​. This cross-cultural fertilization meant that by the later Crusades, all belligerents were fielding similar formidable arsenals. Historian Michael Fulton notes that armies in the Holy Land even began prefabricating siege engine components and stockpiling timber in places like Damascus, reflecting a shared understanding that mobility and preparation were key in a land with scarce wood supplies​. The exchange of knowledge went beyond weaponry: logistics, engineering techniques, and even the concept of military engineering as a specialized skill were disseminated across cultures. The crusading period showed that technology transfer was not a one-way street; both Franks and Saracens benefited from each other’s innovations in the art of war.

The impact of crusader siegecraft is also evident in medieval architecture and infrastructure. Exposure to formidable Near Eastern fortifications prompted Europeans to rethink their own castle designs. Crusaders established states in the Levant and built massive castles like Krak des Chevaliers and Margat, which featured multiple concentric layers of walls, extensive moats, and complex gate systems. These “crusader castles” set new standards for defensive construction. Ideas and experienced engineers traveled back to Europe, contributing to the proliferation of concentric castles and improved urban fortifications in the 13th century​. Meanwhile, in the Islamic world, encounters with Western siege tactics may have accelerated the development or adoption of counterweight trebuchets and other advances. In essence, the Crusades created an arms race of construction and destruction: as siege engines grew more powerful, so did the walls built to oppose them, each spurring the other to new heights (and depths) of ingenuity​. This arms race mirrored the broader clash of civilizations in the Holy Land, where cultures competed not only in faith and valor but also in technical prowess.

Culturally, the prominence of siege warfare in the Crusades left a mark on literature, art, and memory. Medieval chronicles devote extensive sections to sieges, describing in detail the machines and tactics as marvels of the age. These accounts helped turn engineers like those who built the Tower of David siege engines or the mighty trebuchets at Acre into unsung heroes of the narrative. Siege imagery found its way into illuminated manuscripts and church frescoes—often as metaphors for spiritual struggle (the Siege of Jericho or the assault on the Devil’s fortress) but clearly inspired by contemporary events. The idea of perseverance in the face of an unyielding fortress became a moral lesson as much as a military one. In the long term, the Crusades also had the unintended effect of increasing communication and exchange between East and West. Technologies such as gunpowder (transferred via the Mongols and Islamic world to Europe in the 13th–14th centuries) and architectural ideas like the pointed arch (which some scholars associate with Eastern influence) thrived in the climate of curiosity and necessity that the Crusades helped foster. While siege engines themselves would eventually be eclipsed by cannons, the underlying advances in engineering and the habit of innovation would carry forward. A recent quantitative analysis supports the significant impact of these pre-gunpowder technologies: statistical data on sieges from 1097–1291 indicate that the use of torsion and counterweight artillery measurably increased the odds of a successful siege, validating the crucial role of siege engines in medieval warfare​. In other words, the societal investment in technology during the Crusades paid real dividends in military outcomes, reshaping the political and cultural landscape of the Mediterranean world.

Conclusion: engineering faith & fury

Siege machines of the Crusades were more than just tools of destruction—they were symbols of technological ingenuity and societal resolve. This era demonstrated how military necessity can fuel innovation, and how religious fervor can be both a motivator and a justification for scientific and engineering advancement. From the humble ladder to the grand trebuchet and towering siege engines, these weapons defined a critical chapter in medieval history where belief and engineering converged to reshape the world. The Crusaders’ fervent faith did not preclude practical science; on the contrary, it often inspired it, as victories were attributed to divine will but achieved through very tangible mechanical means. The legacy of these innovations influenced medieval warfare for centuries, inaugurating a tradition of military engineering that would continue to evolve with the introduction of gunpowder and beyond. The lessons learned — about logistics, resilience, and the interplay of offense and defense — echo in later eras of warfare. More broadly, the story of siege machines in the Crusades highlights the complex interplay between faith, conflict, and technology. It shows that even in an age defined by spiritual aspirations, it was human craftsmanship and intellect that ultimately carried the day. The relentless arms race between siege engine and fortress left an enduring imprint on society, proving that in the crucible of war, necessity truly is the mother of invention. In the end, the saga of Crusader siegecraft is a testament to human creativity under pressure – a fusion of engineering and ideology that powered both faith and fury.

AI Acknowledgement:

Chat GPT and Microsoft CoPilot were used to come up with chapter structure/outline, mainly for creative paragraph titling and to generate interactive questions from the chapter. After writing the chapter initially, I also used AI briefly to clean up structure and check for chapter flow/grammar. Information including pictures and sources was found by me.

https://chat.openai.com/

https://copilot.cloud.microsoft/

references:

Cartwright, M. (2018, May 24). Siege Warfare in Medieval Europe. World History Encyclopedia. https://www.worldhistory.org/article/1230/siege-warfare-in-medieval-europe/

Cartwright, M. (2018, October 09). The Crusades: Consequences & Effects. World History Encyclopedia. https://www.worldhistory.org/article/1273/the-crusades-consequences–effects/

Lindberg, I. (n.d.). Engineering analysis of siege engines in the First crusade.

Engineering Analysis of Siege Engines in the First Crusade. viewcontent.cgi

Darling, D. (n.d.). Siege machines of the Crusaders. The Worlds of David Darling. Retrieved from http://www.daviddarling.info/encyclopedia_of_history/S/siege_machines_of_Crusaders.html 

Fulton, M. S. (2015). Development of prefabricated artillery during the Crusades. Journal of Medieval Military History, 13, 51–72.

Heller, C.-P. (2024). The impact of siege artillery: Evidence from the Eastern Mediterranean, 1097–1291. SSRN. http://dx.doi.org/10.2139/ssrn.4964486

Image sources

Darling, D. (n.d.). Siege machines of the Crusaders. siege machines of the Crusaders
This image shows the Crusaders besieging Jerusalem in 1099 during the First Crusade, using ladders, mangonels, and an assault shed to breach the city’s defenses while defenders fought back with fire and counterattacks.