From the very outset of the period until the end even simplest defences gave a great advantage to those that held them. A simple wood and earthwork structure could nullify the dominant effects of heavy cavalry and allow small garrison to hold out against a much larger host. As stone fortifications became more common greater siege weapons and techniques had to be utilised, but ultimately the defensive advantage remained. The most effective developments in this period were the improvement of defensive architecture and strategic planning of fortifications.
After the conquest of England by William I the most common form of fortification was the ‘Motte and Baily’ castle. These simple wooden and earthwork forts were attributed by medieval chroniclers such as OrdericVitalis as the reason for the success of the Norman invaders. These defences were quick and easy to construct as timber was readily available in most of Europe and peasant labourers could easily construct them in a relatively short time. The ‘Motte and Baily’ could be located almost anywhere and could easily dominate the surrounding countryside, William I famously brought a pre-fabricated Donjon across the channel in 1066 showing how important these defences were to the Normans. These fortifications were not however a Norman design, they likely came from Flanders and the Low Countries where a simple raised earthwork home could provide a dominating position as well as defence against both enemies and flood water. The effectiveness of ‘Motte and Baily’ castles is demonstrated perfectly by the Siege of Le Puiset in 1111 where the garrison were able to hold out for some time against King Louis VI of France even sallying out and destroying a diversionary attack. Fire was incredibly effective against wooden defences however it was not necessarily easy to get them burning in the first place, at Le Puiset attempts to burn the gate failed. These simple wooden fortifications allowed for a quick establishment of dominance over the land and any potential attackers as well as establishing the basic principle of a castle as a fortified residence, however they could not hold out against a sustained attack and were vulnerable to bombardment. At the turn of the 13th century wooden and earthwork forts were built and used showing the enduring nature of such a simple design.
The main development of defensive architecture in this period was the spread of stone defences. Historical debate has surrounded the extent of the spread of stone fortification, R. Highman and P. Barker suggest that they remained dominant far longer than the works of J. Badbury, J. France and R.A. Brown would suggest. Stone fortifications were already common in drier parts of Sothern Europe such as Spain and Italy, where wood was less readily available, and stone forts existed in Western Europe at the start of our period. Seemingly wooden defences were often redesigned or rebuilt out of stone, although such defences were more expensive and required more skilled labourers, the strength they brought was unquestionable. Stone walls provided a behemoth for besiegers; they could not simply set them alight and wait for them to burn down, they had to be more inventive or patient. Stone defences could easily withstand bombardment from most artillery pieces of the time with mangonels and traction trebuchets unlikely to do significant damage to stone walls. Due to the expensive nature of stone castles the progress of change was slow, only great territorial princes or kings could at first afford to build great castles out of stone; as such most fortifications were converted over generations. In the crusader states concentric castles were being built such as Krak des Chevaliers and Margat, although such designs did not come to England until later in the 13th century. Many fortifications in the west became much larger and began to incorporate tiered defences such as Chateau Gaillard and the improvements made to Dover castle, generally all defensive fortifications increased in size. Stone fortifications came to dominate siege warfare, although wooden fortifications continued to be constructed, it was stone that endured the test of time and can still be seen today.
Castles were not the only focus of sieges; often towns would come under attack and be besieged. When towns were the target of a siege they could be very hard to attack as they were harder to cut off from support than castles and they often contained more people and supplies. Street fighting could also be deadly as defenders could block roads and use town roofs to harass attackers below. It was during the Albigensian crusade that Simon de Montfort was killed while besieging the city of Toulouse. A well-fortified town could be as deadly as a castle however garrisons suffered at the increased risk of disease, starvation and betrayal inside the walls.
Town defences also developed in this period along the same lines as castles, their defences were rebuilt in stone and overall they became much larger. Many towns had a citadel built within them, which would function as the final stage of defence should outer walls be overwhelmed. The use of citadels was similar to the tiered defences that came with the development of ‘concentric’ castle designs suggesting that this was a strategic development made during this period. This may also be attributed to the growth of towns around castles and the use of castles to dominate towns, especially in post conquest England. It should be noted that many towns had a ‘great tower’ which would function as a final place of defence, such as the Tower of David in Jerusalem. The concept of a Citadel was therefore not a true development of this period, however undoubtedly they became more extensive and widespread.
The development of defensive architecture was not the only change in siege warfare during this period however. The way that sieges were conducted changed as well as the people who were involved with them. At the start of the period castle guard duty was a key component of knighthood however over time this was often replaced by a payment which could be used to pay for a permanent garrison. Some of the most important warriors in a garrison were the crossbowmen who could deliver deadly bolts with great accuracy, which the Angevin kings made great use of. Castle garrisons still retained mounted warriors, due to their effectiveness in aggressive defence and in leading sorties against enemies, however besiegers often established their own defences to limit the effect of this. Besieging armies also changed over this period, skilled engineers were needed to build and operate powerful siege weapons and specialist miners would be needed if defences were particularly strong, and kings often went to great lengths to protect their engineers. The development of forces involved in siege warfare during this period was limited, castles would still require reinforcing if they were to hold out for a long time.
The period saw a development in defensive technologies and methods. Castle design was altered to a ‘concentric’ style incorporating tiered defences and there was an increase in the number of round towers that were built. It has been argued that round towers could be viewed as a development of this period. Round towers had several benefit over square ones, they were harder to bombard, they gave a better field of view and they were harder to undermine but possibly the main benefit was that they could be made stronger with a reduced cost, requiring less stone. Round towers did become more popular in France during this period but elsewhere many towers were built in a variety of shapes. Nowhere did circular towers replace square ones altogether and so the advantages of circular towers must be questioned. If circular towers had provided such an overwhelming advantage to defenders over square designs would there not be a clear effort to replace square ones. It seems that resources, style and taste must have had a part to play as even the Muslim east began to replicate western square towers. The increase in circular towers can be seen as a development in this period however its effectiveness is limited by the extent of its spread.
Other developments of defence came from the spread of crenelation, arrow loops and machicolation which helped defenders to harass attackers with less exposure and risk to themselves. Defensive technologies such as these were initially constructed on top of stone walls in wood, but as defensive architecture developed these were directly incorporated into the design allowing for much stronger and better defended walls. Another development, the covered fighting area, can be found in many castles in the crusader states although these did not become widespread in the west during this period. These covered fighting areas allowed defenders to fight without fear of bombardment and became an increasingly popular concept. Defensive technologies such as these helped to maintain the considerable advantage that defenders had over attackers.
Defensive tactics developed little in this period, before a siege began a garrison would need to be reinforced, the defences improved by the construction of wooden hoardings and attempts would be made to enact a scorched earth policy around the castle. By drawing in as many resources to the castle as possible and destroying those that they could not defenders denied the besiegers access to them. Defenders could sally out at opportune moments to harass the enemy and if they caught them off guard this could be devastating, postern gates and other hidden exits were built for this purpose. Defensive artillery could be used to bombard the besiegers and were sometimes mounted on towers to give improved range. The main development in defence was at the architectural level, as defences retained its advantage there was little need to develop defensive tactics.
There were relatively few developments in attacking methods or technology during this period, although those that were made were quite significant. Mangonels, traction trebuchets and ballista were all in regular use at the start of the period; however they stood little chance of doing significant damage to a stone wall and could only damage the tops of towers to any effect. The most widely recognised development of this period was the invention of the counterweight trebuchet, the symbol of medieval siege warfare. These powerful weapons outclassed all other forms of siege equipment able to throw heavier projectiles further and with greater accuracy. After the development of the counterweight trebuchet stone walls were still hard to destroy and it required continual bombardment to destroy a wall by this means alone. Although the counterweight trebuchet is undoubtedly a development of this period it still could not overcome the strength of defensive architecture. Ultimately besiegers still had to rely on close assault to take a castle by force as artillery was incapable of destroying all defences.
Other developments also occurred in this period which aided attackers. ‘Greek fire’ had been used in the east by the Byzantine empire as well as the Muslim states, attempts at recreating sticky fire in the west were often met with limited success but it was used nonetheless. Even as castle towers and walls became increasingly well defended the gate often remained as a weak point which could be the focal point of attacks, in this sense fire was still a very useful tool and remained important for attackers. ‘Greek Fire’ could be devastating however in reality it was rarely as effective as its potential suggested.
Mining was used extensively in medieval sieges and was one of the deadliest tools in an attacker’s arsenal. This was rightly feared by many garrisons and its devastating effect is amply shown at the siege of Rochester castle in 1215. The only effective defence against mining was a deep and wide moat as attempts to countermine which could run the risk of accidently collapsing your own defences. Siege towers are also an iconic image of the medieval siege. These were beneficial as they provided a great firing position for archers, crossbowmen and stone throwers as well as being able to directly assault a section of wall with far greater forces than scaling ladders. Siege towers had been used well before our period and continued in use afterwards, these got larger in response to the increasing size of defences. Rams, picks and bores were all used to attack walls and gates in an attempt to hammer ones way through the defences, with the addition of a movable ‘penthouse’ these became very effective. Such equipment was often referred to as a ‘cat’ due to their slow but potentially deadly advance. These methods and technologies were not truly developments of this period as they became more widespread merely in response to the increase of stone fortifications. Such tools became no more effective during this period that it had been prior to it.
Developments in siege warfare also came at a more strategic level. Medieval warfare was centred on land ownership and as such castles were initially built near the land which the individual directly held. Theses fortifications could be used to defend private estates or to attack those of others however consideration was rarely given for anything beyond a local scale. Over this period we see a marked shift towards building fortifications in more strategic locations and in stronger geographical positions as kings began to rely less on the local nobility to fortify important areas such as the Norman Vexin. More often castle came to be built to dominate river crossings, control important marches and make striking statements of dominance as seen at Chateau Gaillard. Fortifications such as these never formed a ‘frontline’ of defences, they were permeable boundaries which could be crossed, but an interlinking series of fortifications could present and incredibly hard target to take. No matter how strong an individual fortification may be if they were cut off from support they soon fell, these systems of defences had to be supported by field armies and other castles in order to hold out for a long time. The strategic planning of fortifications is therefore an incredibly important development in siege warfare during this period. Although the fighting of sieges themselves may not have changed dramatically by rethinking where defences should be built and how they could be used siege warfare was altered.
The most effective development of siege warfare was the spread of stone castles. Improvements to offensive artillery were simply not enough to overcome the massive improvement in defensive architecture. As stone fortifications became increasingly larger it was ever more difficult for sieges to be brought to a quick conclusion. Failure to develop new attacking methods meant that besiegers had to rely on starvation and surrender to ensure victory. By combining these developments in defensive architecture with strategic planning monarchs found it easier to ensure the defence of the realm. The defensive advantage was so great throughout this period that warfare took on an inherently defensive and cautious nature in contrary to popular belief of reckless, wild, chivalric hot headedness; no developments in this period would change that.
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