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A siege is a prolonged military assault and blockade on a city
or fortress with the intent of conquering by force or attrition. A siege occurs when an attacking army encounters a city or fortress that refuses to surrender
and cannot be taken by a frontal assault. Sieges usually involve
surrounding the target and blocking the provision of supplies, typically coupled with artillery bombardment, sapping and mining to reduce fortifications.
Sieges are as old as warfare itself, with towns in the Middle East from
the dawn of civilization having city walls. During the Renaissance and the Early
Modern period, siege warfare dominated the conduct of war in Europe. Campaigns were generally designed around a succession of
sieges until the Napoleonic period. In modern times, trenches have replaced walls, and bunkers have replaced
castles. At the same time, the significance of the classical siege has declined. With the advent of mobile warfare, one single
fortified stronghold is no longer as decisive as it once was. While sieges do still occur, they are not as common as they once
were due to recent changes in modes of battle.
Ancient and medieval siege warfare
Ancient sources contain many stories of sieges, such as the siege of Jericho in
the Old Testament or the siege of Troy described by Homer in the Iliad. An astonishing number and variety of sieges formed the core of Julius Caesar's conquest of Gaul.
The universal method for defending against siege is the use of fortifications, principally walls and ditches. A sufficient
supply of food and water is also important to defeat the simplest method of siege warfare: starvation. During a siege, a surrounding army could easily prevent food and water supplies from reaching the
besieged city. If the siege lasted long enough, defenders and civilians might have been reduced to eating anything vaguely
edible—family pets, the leather from shoes, and even each other.
Various methods were developed to counter fortifications in ancient and medieval times. Ladders could be used to escalade over the defences; walls could be
broken down by launching projectiles at them, or could be made to collapse by mining under the walls. Alternatively, the
defenders could be forced into submission by means of starvation or illness.
A large variety of siege engines were developed for use by besieging
armies. Battering rams could be used to force through gates or walls,
while catapults, ballistae, trebuchets, mangonels, and onagers could be used to launch projectiles in order to
compromise a city's fortifications and kill its defenders. The siege tower
was a substantial structure built by the attackers outside of the defences, overlooking the walls, which allowed the attackers to
fire down upon the defenders.
In addition to launching projectiles at the fortifications or defenders, it was also quite common to attempt to undermine the
fortifications, causing them to collapse. This could be accomplished by digging a tunnel beneath the foundations of the walls, and then deliberately
collapsing or exploding the tunnel. This process is known as sapping.
Fire was often used as a weapon when dealing with wooden fortifications. In ancient Japan, where buildings used to store supplies were mostly wooden, a fire could drive opponent to a starvation. The
Byzantine Empire invented Greek fire, which contained additives that made it hard to put out. Combined with a primitive flamethrower, it proved an effective offensive and defensive weapon.
Cahir Castle in Ireland
Advances in the prosecution of sieges in ancient and medieval times naturally encouraged the development of a variety of
defensive counter-measures. In particular, medieval
fortifications became progressively stronger—for example, the advent of the concentric castle from the period of the Crusades—and
more dangerous to attackers—witness the increasing use of machiolations and murder-holes, as well the preparation of
boiling oil. Arrow slits, secret access points and deep water wells were also integral means of
resisting siege at this time. Particular attention would be paid to defending entrances, with gates protected by drawbridges, portcullises and
barbicans.
In the European Middle Ages, virtually all large cities had city
walls—Dubrovnik in Dalmatia
is an impressive and well-preserved example—and more important cities had citadels, forts or castles. Great
effort was expended to ensure a good water supply inside the city in case of siege. In some cases, long tunnels were constructed
to carry water into the city. Complex systems of underground tunnels were used for storage and communications in medieval cities
like Tįbor in Bohemia (similar to those
used much later in Vietnam during the Vietnam War).
Until the invention of gunpowder-based weapons (and the resulting
higher-velocity projectiles), the balance of power and logistics definitely favored the defender. With the invention of
gunpowder, cannon and (in modern times) mortars and howitzers, the traditional methods of defense
became less and less effective against a determined siege.
Mongol siege warfare
In the Middle Ages, the Mongol Empire's campaign against China by Genghis Khan and his army was
extremely effective, allowing the Mongol hordes to sweep through large areas. Even if they could not enter some of the more
well-fortified cities, they used innovative battle tactics to grab hold of the land and the people:
- "By concentrating on the field armies, the strongholds had to wait. Of course, smaller fortresses, or ones easily
surprised, were taken as they came along. This had two effects. First, it cut off the principal city from communicating with
other cities where they might expect aid. Secondly, refugees from these smaller cities would flee to the last stronghold. The
reports from these cities and the streaming hordes of refugees not only reduced the morale of the inhabitants and garrison of the
principle city, it also strained their resources. Food and water reserves were taxed by the sudden influx of refugees. Soon, what
was once a formidable undertaking became easy. The Mongols were then free to lay siege without interference of the field army as
it had been destroyed... At the siege of Aleppo, Hulegu used twenty catapults against the Bab al-Iraq (Gate of Iraq) alone. In Jūzjānī, there are several
episodes in which the Mongols constructed hundreds of siege machines in order to surpass the number which the defending city
possessed. While Jūzjānī surely exaggerated, the improbably high numbers which he used for both the Mongols and the defenders do
give one a sense of the large numbers of machines used at a single siege." 1
Another Mongol tactic was to use catapults to launch corpses of plague victims into
besieged cities. The disease-carrying fleas from the person's body would then infest the
city, and the plague would spread allowing the city to be easily captured, although this transmission mechanism was not known at the time. On the first night while sieging a city, the
leader of the Mongol forces would lead from a white tent: if the city surrendered, all
would be spared. On the second day, he would use a red tent: if the city surrendered, the men would all be killed, but the rest
would be spared. On the third day, he would use a black tent: no quarter would be given.
Sieges in the age of gunpowder
The introduction of gunpowder and the use of siege cannons brought about a new age in
siege warfare. The greatest advantage of cannons over other siege weapons was the ability to concentrate a weight of fire on a
single point on a wall with great accuracy. Thus, more vulnerable points in defensive walls were exploited and reduced to ruins
in a short amount of time, rendering the military architecture of the day ineffective.
New fortifications, designed to withstand gunpowder weapons were constructed throughout Europe and came to dominate urban
architecture. During the Renaissance and the Early Modern period, siege warfare dominated the conduct of war in Europe.
Emerging theories on improving fortifications
The castles that in earlier years had been formidable obstacles were easily breached by the new weapons. For example, in
Spain, the newly equipped army of Ferdinand and
Isabella was able to conquer Moorish strongholds in Granada in 1482-92 that had held out for centuries before the invention of cannons.
In the early 15th century, Italian architect Leon Battista
Alberti wrote a treatise entitled De Re aedificatoria which theorized methods of building fortifications capable of
withstanding the new guns. He proposed that walls be "built in uneven lines, like the teeth of a saw." He proposed star-shaped
fortresses with low thick walls.
However, few rulers paid any attention to his theories. A few towns in Italy began building in the new style late in the
1480s, but it was only with the French invasion of the Italian peninsula in 1494-95 that the new fortifications were built on a
large scale. Charles VIII invaded Italy with an army of
18,000 men and a horse-drawn siege-train. As a result he could defeat virtually any city or state, no matter how well defended. In a panic,
military strategy was completely rethought throughout the Italian states of the time, with a strong emphasis on the new
fortifications that could withstand a modern siege.
New styles of fortresses employed
The most effective way to protect walls against cannon fire proved to be depth (increasing the width of the defences) and
angles (ensuring that attackers could only fire on walls at an oblique angle, not square on). Star-shaped fortresses surrounding
towns and even cities with outlying defenses proved very difficult to capture, even for a well equipped army. The new style of
fortress became known as the trace italienne. Fortresses
built in this style throughout the 16th century did not become fully
obsolete until the 19th century, and were still in use throughout World War I
(though modified for 20th century warfare).
However, the cost of building such vast modern fortifications was incredibly high, and was often too much for individual
cities to undertake. Many were bankrupted in the process of building them; others, such as Siena, spent so much money on fortifications that they were unable to maintain their armies properly, and so lost
their wars anyway. Nonetheless, innumerable large and impressive fortresses were built throughout northern Italy in the first
decades of the 16th century to resist repeated French invasions that became known as the Wars of Italy. Many stand to this
day.
In the 1530s and 1540s, the new style of
fortification began to spread out of Italy into the rest of Europe, particularly to France, the Netherlands, and Spain. Italian engineers were in enormous demand throughout Europe, especially in
war-torn areas such as the Netherlands, which became dotted by towns encircled in modern fortifications. For many years,
defensive and offensive tactics were well balanced leading to protracted and costly wars such as Europe had never known,
involving more and more planning and government involvement.
The new fortresses ensured that war rarely extended beyond a series of sieges. Because the new fortresses could easily hold
10,000 men, an attacking army could not ignore a powerfully fortified position without serious risk of counterattack. As a
result, virtually all towns had to be taken, and that was usually a long drawn out affair, potentially lasting from several
months to years, while the members of the town were starved to death. Most battles in this period were between besieging armies
and relief columns sent to rescue the besieged.
Marshall Vauban
A pentagonal Vauban fortress
At the end of the 17th century, Marshal Vauban, a French military engineer, developed modern fortification to its
pinnacle, refining siege warfare without fundamentally altering it: ditches would be dug; walls would be protected by glacis; and bastions would enfilade an attacker. He was also a master of planning sieges themselves. Before Vauban, sieges had been
somewhat slapdash operations. Vauban refined besieging to a science with a methodical process that, if uninterrupted, would break
even the strongest fortifications.
Planning and maintaining a siege is just as difficult as fending one off. A besieging army must be prepared to repel both
sorties from the besieged area and also any
attack that may try to relieve the defenders. It was thus usual to construct lines of trenches and defenses facing in both
directions. The outermost lines, known as the lines of circumvallation, would surround the entire besieging army and protect it from attackers. This would be the
first construction effort of a besieging army, built soon after a fortress or city had been invested. A line of contravallation would also be constructed, facing in towards the besieged
area, to protect against sorties by the defenders and to prevent the besieged from escaping.
The next line, which Vauban usually placed at about 600 meters from the target, would contain the main batteries of heavy
cannons so that they could hit the target without being vulnerable themselves. Once this line was established, work crews would
move forward creating another line at 250 meters. This line contained smaller guns. The final line would be constructed only 30
to 60 meters from the fortress. This line would contain the mortars and would act as a staging area for attack parties once the walls were breached. It would also be
from there that sappers working to undermine the fortress would operate.
The trenches connecting the various lines of the besiegers could not be built perpendicular to the walls of the fortress, as
the defenders would have a clear line of fire along the whole trench. Thus, these lines (known as saps) needed to be
sharply jagged.
Another element of a fortress was the citadel. Usually a citadel was a "mini
fortress" within the larger fortress, sometimes designed as a last bastion of defense, but more often as a means of protecting
the garrison from potential revolt in the city. The citadel was used in wartime and peacetime to keep the residents of the city
in line.
As in ages past, most sieges were decided with very little fighting between the opposing armies. An attacker's army was poorly
served incurring the high casualties that a direct assault on a fortress would entail. Usually they would wait until supplies
inside the fortifications were exhausted or disease had weakened the defenders to the
point that they were willing to surrender. At the same time, diseases, especially typhus were a constant danger to the encamped armies outside the fortress, and often forced a premature retreat.
Sieges were often won by the army that lasted the longest.
An important element of strategy for the besieging army was whether or not to
allow the encamped city to surrender. Usually it was preferable to graciously allow a surrender, both to save on casualties, and to set an example for future defending cities. A city that was allowed
to surrender with minimal loss of life was much better off than a city that held out for a long time and was brutally butchered
at the end. However, if an attacking army had a reputation of killing and pillaging regardless of a surrender, then other cities'
defensive efforts would be redoubled.
Siege warfare dominated in Western Europe for most of the seventeenth
and eighteenth centuries, but this pattern was eradicated by the French Revolutionary and Napoleonic Wars. New techniques stressed rapidly moving armies that would clash on the open field of
battle, and one single fortified stronghold was no longer as decisive as it used to be. Advances in artillery made previously
impregnable defenses useless. For example, the walls of Vienna that
had held off the Turks in the mid-seventeenth century were no obstacle
to Napoleon in the late eighteenth. Where sieges occurred, the attackers were
usually able to defeat the defences within a matter of days or weeks, rather than weeks or months as previously. This era of
rapidly moving armies continued through the 19th century, reaching its peak
in the Franco-Prussian War. For example, the great Swedish
white-elephant fortress of Karlsborg was built in the tradition of Vauban and
intended as a reserve capital for Sweden, but it was obsolete before it was completed in 1869.
Modern warfare
Mainly as a result of the increasing firepower (such as machine guns)
available to defensive forces, First World War trench warfare briefly revived a form of siege warfare. Although siege warfare had moved out from an
urban setting because city walls had become ineffective against modern weapons, trench warfare was nonetheless able to utilize
many of the techniques of siege warfare in its prosecution (sapping, mining, barrage and, of course, attrition) but on a much
larger scale and on a greatly extended front. The development of the armoured tank at the
end of World War I swung the pendulum back in favour of maneuver.
The Blitzkrieg of the Second World War truly showed that fixed fortifications are easily defeated by maneuver instead of frontal
assault or long sieges. Battles that would have taken weeks of siege could now be avoided with the careful application of air
power (such as the German paratrooper capture of Fort Eban, Belgium, early in World War II). The
most important sieges of the Second World War were on the Eastern Front where bloody urban warfare marked the battles of Leningrad and Stalingrad. In these battles, the ruins of an urban landscape proved to be just as effective an
obstacle to an advancing army as any fortifications.
During the Vietnam War the battles of Dien Bien Phu (1954) and Khe Sanh (1968) possessed siege-like characteristics. In both cases, the Vietcong were able to cut off the opposing army by capturing the surrounding rugged terrain. At Dien Bien
Phu, the French were unable to use air power to overcome the siege and were defeated. But at Khe Sanh a mere 14 years later,
advances in air power allowed the United States to overcome the siege and
win the battle.
Police actions
Despite the overwhelming might of the modern state, siege tactics continue to be employed in police conflicts. This has been due to a number of factors, primarily risk to life, whether that of the police, the
besieged, bystanders or hostages. Police make use of trained negotiators, psychologists and, if
necessary, force, generally being able to rely on the support of their nation's armed forces if required. Unlike traditional military sieges, police sieges tend to last for hours or days
rather than weeks, months or years.
See also
References
- May, Timothy. "Mongol Arms ." Explorations in Empire,
Pre-Modern Imperialism Tutorial: the Mongols. University of Wisconsin-Madison. 27 June 2004.
Further reading
- Duffy, Christopher. Fire & Stone: The Science of Fortress Warfare (1660–1860). 1975. 2nd ed. New York:
Stackpole Books, 1996.
- Duffy, Christopher. Siege Warfare: Fortress in the Early Modern World, 1494–1660. Routledge and Kegan Paul,
1996.
- Duffy, Christopher. Siege Warfare, Volume II: The Fortress in the Age of Vauban and Frederick the Great. Routledge
and Kegan Paul: London, 1985.
- Lynn, John A. The Wars of Louis XIV.
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