Sieges probably predate the development of cities as large population centers. Ancient cities in the Middle East show archaeological evidence of having had fortified city walls. During the Warring States era of ancient China, there is both textual and archaeological evidence of prolonged sieges and siege machinery used against the defenders of city walls. Siege machinery was also a tradition of the ancient Greco-Roman world. During the Renaissance and the Early Modern period, siege warfare dominated the conduct of war in Europe. Leonardo da Vinci gained as much of his renown from the design of fortifications as from his artwork.
Medieval campaigns were generally designed around a succession of sieges. In the Napoleonic era, increasing use of ever more powerful cannon reduced the value of fortifications. In modern times, trenches replaced walls, and bunkers replaced castles. In the 20th century, the significance of the classical siege 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 changes in modes of battle, principally the ease by which huge volumes of destructive power can be directed onto a static target. Sieges in present day are more commonly either smaller hostage, militant, or extreme resisting-arrest situations such as the Waco Siege.
Generally speaking, siege warfare is a form of low-intensity warfare (until an assault takes place) characterized in that at least one party holds a strong defense position, it is highly static situation, the element of attrition is typically strong and there are plenty of opportunities for negotiations.
Some settlements in the Indus Valley Civilization were also fortified. By about 3500 B.C., hundreds of small farming villages dotted the Indus floodplain. Many of these settlements had fortifications and planned streets. The stone and mud brick houses of Kot Diji were clustered behind massive stone flood dikes and defensive walls, for neighboring communities quarreled constantly about the control of prime agricultural land. Mundigak (c. 2500 B.C.) in present day south-east Afghanistan has defensive walls and square bastions of sun dried bricks.
City walls and fortifications were essential for the defense of the first cities in the ancient Near East. The walls were built by mud bricks, stone, wood or a combination of these materials depending on local availability. City walls may also have served the dual purpose of showing presumptive enemies the might of the Kingdom. The great walls surrounding the Sumerian city of Uruk gained such a wide-spread reputation. The walls were 9.5 km / 6 miles in length, and raised up to 12 metres / 40 feet in height. Later the walls of Babylon, reinforced by towers and moats, gained a similar reputation. In Anatolia, the Hittites built massive stone walls around their cities, taking advantage of the hillsides. In Shang Dynasty China, at the site of Ao, large walls were erected in the 15th century BC that had dimensions of 20 meters / 65 feet in width at the base and enclosed an area of some squared. In similar dimensions, the ancient Chinese capital for the State of Zhao, Handan (founded in 386 BC), had walls that were again 20 meters / 65 feet wide at the base, a height of 15 meters / 50 feet tall, with two separate sides of its rectangular enclosure measured at a length of . The cities of the Indus Valley civilization showed less effort in constructing defenses, and likewise the Minoan civilization on Crete. These civilizations probably relied more on the defense of their outer borders or sea shores. Unlike the ancient Minoan civilization, the Mycenaean Greeks emphasized need for fortifications alongside natural defenses of mountainous terrain, such as the massive 'Cyclopean' walls built at Mycenae during the last half of the 2nd millennium BC.
Although there are depictions of sieges from the ancient Near East in the historical sources and in ancient Near Eastern art, there are very few examples of siege systems that have been found archaeologically. Of the few examples, several are noteworthy:
1) The late 9th cent. BCE siege system surrounding Tell es-Safi/Gath, Israel. This system, which is comprised of a 2.5 km long siege trench, towers and other elements, the earliest evidence of a circumvallation system known in the world, was apparently built by Hazael of Aram Damascus, as part of his siege and conquest of Philistine Gath in the late 9th cent. BCE (mentioned in II Kings 12:18).
2) The late 8th cent. BCE siege system surrounding the site of Lachish (Tell el-Duweir) in Israel. This system, which was built by Sennacherib of Assyria in 701 BCE, is not only evident in the archaeological remains, but is described in the Assyrian and biblical sources and in the reliefs of Sennacherib's palace in Nineveh.
The earliest representations of siege warfare is dated to the Protodynastic Period of Egypt, c.3000 BC. These show symbolic destruction of city walls by divine animals using hoes. The first siege equipment is known from Egyptian tomb reliefs of the 24th century BC, showing Egyptian soldiers storming Canaanite town walls on wheeled siege ladders. Later Egyptian temple reliefs of the 13th century BC portrays the violent siege of Dapur, a Syrian city, with soldiers climbing scale ladders supported by archers. Assyrian palace reliefs of the 9th to 7th centuries BC display sieges of several Near Eastern cities. Though a simple battering ram had come into use in the previous millennium, the Assyrians improved siege warfare and built huge wooden tower shaped battering rams with archers positioned on top. In ancient China, sieges of city walls (along with naval battles) were portrayed on bronze 'hu' vessels dated to the Warring States (5th century BC to 3rd century BC), like those found in Chengdu, Sichuan, China in 1965.
The most common practice of siege warfare was however to lay siege and wait for the surrender of the enemies inside. The Egyptian siege of Megiddo in the 15th century BC lasted for 7 months before its inhabitants surrendered. The Hittite siege of a rebellious Anatolian vassal in the 14th century BC ended when the queen mother came out of the city and begged for mercy on behalf of her people. If the main objective of a campaign was not the conquest of a particular city, it could simply be passed by. The Hittite campaign against the kingdom of Mitanni in the 14th century BC bypassed the fortified city of Carchemish. When the main objective of the campaign had been fulfilled, the Hittite army returned to Carchemish and the city fell after an eight-day-siege. The well-known Assyrian Siege of Jerusalem in the 8th century BC came to an end when the Israelites bought them off with gifts and tribute, according to the Assyrian account, or when the Assyrian camp was struck by mass death, according to the Biblical account. Due to the problem of logistics, long lasting sieges involving but a minor force could seldom be maintained.
During the Warring States (481–221 BC) era of China, warfare lost its honorable, gentlemen's duty that was found in the previous era of China (Spring and Autumn period), and became more practical, competitive, cut-throat, and efficient for gaining victory. The Chinese invention of the hand-held, trigger-mechanism crossbow during this period revolutionized warfare, giving greater emphasis to infantry and cavalry and less to traditional chariot Chinese warfare. The philosophically-pacifist Mohists (followers of the philosopher Mozi) of the 5th century BC believed in aiding the defensive warfare of smaller Chinese states against the hostile offensive warfare of larger domineering states. The Mohists were renowned in the smaller states (and the enemies of the larger states) for the inventions of siege machinery to scale or destroy walls. This included traction trebuchet catapults, eight foot high ballistas, a wheeled siege ramp with grappling hooks known as the Cloud Bridge (the protractable, folded ramp slinging forward by means of a counterweight with rope and pulley), and wheeled 'hook-carts' used to latch large iron hooks onto the tops of walls to pull and tear them down. When enemies attempted to dig tunnels under walls for mining or entry into the city, the defenders used large bellows (the type the Chinese commonly used in heating up the blast furnace for smelting cast iron) to pump smoke into the tunnels in order to suffocate the intruders.
The universal method for defending against siege is the use of fortifications, principally walls and ditches to supplement natural features. 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 would build earthworks (a line of circumvallation) to completely encircle their target, preventing food and water supplies from reaching the besieged city. If sufficiently desperate as the siege progressed, defenders and civilians might have been reduced to eating anything vaguely edible—horses, family pets, the leather from shoes, and even each other. On occasion, the defenders would drive 'surplus' civilians out to reduce the demands on stored food and water.
Disease was another effective siege weapon, although the attackers were often as vulnerable as the defenders. In some instances, catapults or like weapons would fling diseased animals over city walls in an early example of biological warfare.
To end a siege more rapidly various methods were developed in ancient and medieval times to counter fortifications, and a large variety of siege engines were developed for use by besieging armies. Ladders could be used to escalade over the defenses. Battering rams and siege hooks 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 break down a city's fortifications and kill its defenders. A siege tower could also be used: a substantial structure built as high, or higher than the walls, it allowed the attackers to fire down upon the defenders and also advance troops to the wall with less danger than using ladders.
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 mining. The defenders could dig counter-tunnels to cut into the attackers' works and collapse them prematurely.
Fire was often used as a weapon when dealing with wooden fortifications. The Byzantine Empire used 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.
If all else failed, a besieger could claim the booty of his conquest undamaged, and retain his men and equipment intact, for the price of a well-placed bribe to a disgruntled gate-keeper.
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 machicolations and murder-holes, as well the preparation of hot or incendiary substances. Arrow slits (also called arrow loops or loopholes), sally ports (airlock like doors) for sallies, 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. Moats and other water defenses, whether natural or augmented, were also vital to defenders.
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 Tábor 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.
Although there are numerous ancient accounts of cities being sacked, few contain any clues to how this was achieved. Some popular tales existed on how the cunning heroes succeeded in their sieges. The best-known is the Trojan Horse of the Trojan War, and a similar story tells how the Canaanite city of Joppa was conquered by the Egyptians in the 15th century BC. The Biblical Book of Joshua contains the story of the miraculous Battle of Jericho. A better detailed historical account from the 8th century BC, called the Piankhi stela, records how the Nubians laid siege to and conquered several Egyptian cities using battering rams, archers, slingers and building causeways across moats.
Alexander the Great's Macedonian army successfully besieged many powerful cities during his astounding conquests. Two of his most impressive achievements in siegecraft took place at Siege of Tyre and the Sogdian Rock. Most conquerors before him had found Tyre, a Phoenician island-city about 1 km from the mainland, impregnable. The Macedonians built a mole, a raised spit of earth across the water, by piling stones up on a natural land bridge that extended underwater out to the island. Alexander's engineers built a causeway that was originally 60 m (200 ft) wide, that reached the range of his torsion-powered artillery. Alexander's soldiers pushed siege towers housing stone throwers and light catapults to bombard the city walls. Though the Tyrians rallied by sending a fire-bombed ship to destroy the towers, and captured the mole in a swarming frenzy, the city eventually fell to the Macedonians after a seven month siege. In complete contrast to Tyre, Sogdian Rock was captured by stealthy attack. Alexander used commando-like tactics to scale the cliffs and capture the high ground. The demoralized defenders surrendered.
The importance of siege warfare in the ancient period should not be underestimated. One of the contributing causes of Hannibal's inability to defeat Rome was his lack of siege train; thus, while he was able to defeat Roman armies in the field, he was unable to capture Rome itself.
The legionary armies of the Roman Republic and Empire are noted as being particularly skilled and determined in siege warfare. An astonishing number and variety of sieges, for example, formed the core of Julius Caesar's mid-1st century BCE conquest of Gaul (modern France). In his Gallic Wars, Caesar describes how at the Battle of Alesia the Roman legions created two huge fortified walls around the city. The inner circumvallation, , held in Vercingetorix's forces, while the outer contravallation kept relief from reaching them. The Romans held the ground in between the two walls. The besieged Gauls, facing starvation, eventually surrendered after their relief force met defeat against Caesar's auxiliary cavalry.
Another Mongol tactic was to use catapults to launch corpses of plague victims into besieged cities. The disease-carrying fleas from the bodies 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 laying siege to 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.
However, the Chinese weren't completely defenseless, and from 1234 until 1279 AD the Southern Song Chinese held out against the enormous barrage of Mongol attacks. Much of this success in defense lay in the world's first use of gunpowder (ie. with early flamethrowers, grenades, firearms, cannons, and land mines) to fight back against the Khitans, the Tanguts, the Jurchens, and then the Mongols. The Chinese of the Song period also discovered the explosive potential of packing hollowed cannonball shells with gunpowder. Written later around 1350 in the Huo Long Jing, this manuscript of Jiao Yu recorded an earlier Song-era cast-iron cannon known as the 'flying-cloud thunderclap eruptor' (fei yun pi-li pao). The manuscript stated that (Wade-Giles spelling):
The shells (phao) are made of cast iron, as large as a bowl and shaped like a ball. Inside they contain half a pound of 'magic' gunpowder (shen huo). They are sent flying towards the enemy camp from an eruptor (mu phao); and when they get there a sound like a thunder-clap is heard, and flashes of light appear. If ten of these shells are fired successfully into the enemy camp, the whole place will be set ablaze...
During the Ming Dynasty (1368–1644 AD), the Chinese were very concerned with city planning in regards to gunpowder warfare. The site for constructing the walls and the thickness of the walls in Beijing's Forbidden City were favored by the Chinese Yongle Emperor (r. 1402–1424), because they were in pristine position to resist cannon volley and were built thick enough to withstand attacks from cannon fire.
For more see Technology of the Song Dynasty.
The greatest advantage of cannons over other siege weapons was the ability to fire a heavier projectile, further, faster and more often than previous weapons. They could also fire projectiles in a straight line, so that they could destroy the bases of high walls. Thus, 'old fashioned' walls—that is high and, relatively, thin—were excellent targets and, over time, easily demolished. In 1453, the great walls of Constantinople were broken through in just six weeks by the 62 cannon of Mehmet II's army.
However, new fortifications, designed to withstand gunpowder weapons, were soon constructed throughout Europe. During the Renaissance and the Early Modern period, siege warfare continued to dominate the conduct of war in Europe.
Once siege guns were developed the techniques for assaulting a town or a fortress became well known and ritualized. The attacking army would surround a town. Then the town would be asked to surrender. If they did not comply the besieging army would surround the town with temporary fortifications to stop sally from the stronghold or relief getting in. The attackers would then build a length of trenches parallel to the defences and just out of range of the defending artillery. They would then dig a trench towards the town in a zigzag pattern so that it could not be enfiladed by defending fire. Once within artillery range another parallel trench would be dug with gun emplacements. If necessary using the first artillery fire for cover this process would be repeated until guns were close enough to be laid accurately to make a breach in the fortifications. In order to allow the forlorn hope and support troops to get close enough to exploit the breach, more zigzag trenches could be dug even closer to the walls with more parallel trenches to protect and conceal the attacking troops. After each step in the process the besiegers would ask the besieged to surrender. If the forlorn hope stormed the breach successfully the defenders could expect no mercy.
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.
This design matured into the trace italienne. Star-shaped fortresses surrounding towns and even cities with outlying defenses proved very difficult to capture, even for a well equipped army. 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 Italian Wars. 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.
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 himself. 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 contravallation, 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 circumvallation 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 miners 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. Moreover, if an attacking army had a reputation of killing and pillaging regardless of a surrender, then other cities' defensive efforts would be redoubled.
The exception to this rule were the English. During the English Civil War anything which tended to prolong the struggle, or seemed like want of energy and avoidance of a decision, was bitterly resented by the men of both sides. In France and Germany, the prolongation of a war meant continued employment for the soldiers, but in England:
This passage from the Memoirs of a Cavalier, ascribed to Daniel Defoe, though not contemporary evidence, is an admirable summary of the character of the Civil War. Even when in the end a regular professional army developed, the original decision-compelling spirit permeated the whole organisation as was seen when pitched against regular professional continental troops the Battle of the Dunes during the Interregnum.
Sixty year later during the War of the Spanish Succession the Duke of Marlborough preferred to engage the enemy in pitched battles rather than engage in siege warfare, although he was very proficient in both types of warfare.
In the early nineteenth century, two factors changed this method of warfare.
Railways, when they were introduced, made possible the movement and supply of larger armies than those that fought in the Napoleonic Wars. It also reintroduced siege warfare, as armies seeking to use railway lines in enemy territory were forced to capture fortresses which blocked these lines. During the Franco-Prussian War, the battlefield front-lines moved rapidly through France. However, the Prussian and other German armies were delayed for months at the Siege of Metz and the Siege of Paris, due to the greatly increased firepower of the defending infantry, and the principle of detached or semi-detached forts with heavy-caliber artillery. This resulted in the later construction of fortress works across Europe such as the massive fortifications at Verdun. It also led to the introduction of tactics which sought to induce surrender by bombarding the civilian population within a fortress rather than the defending works themselves.
The Siege of Sevastopol (1854–1855) during the Crimean War and the Siege of Petersburg (1864–1865) during the American Civil War showed that modern citadels, when improved by improvised defences, could still resist an enemy for many months. The Siege of Pleven during the Russo-Turkish War (1877–1878) proved that hastily-constructed field defences could resist attacks prepared without proper resources, and were a portent of the trench warfare of World War I.
Advances in firearms technology without the necessary advances in battlefield communications gradually led to the defense again gaining the ascendancy. An example of siege during this time, prolonged during 337 days due to the isolation of the surrounded troops, was the Siege of Baler, in which a reduced group of Spanish soldiers, was besieged in a small church by the Philippine rebels, in the course of the Philippine Revolution and the Spanish-American War, until months after the Treaty of Paris, the end of the conflict.
Furthermore, the development of steamships availed greater speed to blockade runners, ships with the purpose of bringing cargo, e.g. food, to cities under blockade, as with Charleston, South Carolina during the American Civil War.
More traditional sieges of fortifications took place in addition to trench sieges. The Siege of Tsingtao was one of the first major sieges of the war, but the inability for significant resupply of the German garrison made it a relatively one sided battle. The Germans and the crew of an Austro-Hungarian protected cruiser put up a hopeless defense and after holding out for more than a week surrendered to the Japanese, forcing the German East Asia Squadron to steam towards South America for a new coal source.
The other major siege outside Europe during the First World War was in Mesopotamia, at the Siege of Kut. After a failed attempt to move on Baghdad, stopped by the Ottomans at the bloody Battle of Ctesiphon, the British and their large contingent of Indian sepoy soldiers were forced to retreat to Kut, where the Ottomans under German General Baron Colmar von der Goltz laid siege. The British attempts to resupply the force via the Tigris river failed, and rationing was complicated by the refusal of many Indian troops to eat cattle products. By the time the garrison fell on 29 April 1916, starvation was rampant. Conditions did not improve greatly under Turkish imprisonment. Along with the Battle of Tanga, the Battle of Sandfontein, the Battle of Gallipoli and the Battle of Namakura, it would be one of Britain's numerous embarrassing colonial defeats of the war.
The largest sieges of the war, however, took place in Europe. The initial German advance into Belgium produced four major sieges, the Battle of Liege, the Battle of Namur, the Siege of Maubeuge and the Siege of Antwerp. All three would prove crushing German victories, at Liege and Namur against the Belgians, at Maubeuge against the French and at Antwerp against a combined Anglo-Belgian force. The weapon that made these victories possible were the German Big Berthas and the Skoda 305 mm Model 1911 siege mortars on loan from Austria-Hungary. These huge guns were the decisive weapon of siege warfare in the 20th century, taking part at Przemysl, the Belgian sieges, on the Italian Front and Serbian Front, and even being reused in World War II.
At the second Siege of Przemysl the Austro-Hungarian garrison showed an excellent knowledge of siege warfare, not only waiting for relief, but sending sorties into Russian lines and employing an active defense that resulted in the capture of the Russian General Kornilov. Despite its excellent performance, the garrison's food supply had been requisitioned for earlier offensives, a relief expedition was stalled by the weather, ethnic rivalries flared up between the defending soldiers and a breakout attempt failed. When the commander of the garrison Hermann Kusmanek finally surrendered, his troops were eating their horses and the first attempt of large scale air supply had failed. It was one of the few great victories obtained by either side during the war, 110,000 Austro-Hungarian prisoners were marched back to Russia. Use of aircraft for siege running, bringing supplies to areas under siege, would nevertheless prove useful in many sieges to come.
The largest siege of the war, and the arguably the roughest, most gruesome battle in history, was the Battle of Verdun. Whether the battle can be considered true siege warfare is debatable. Under the theories of Erich von Falkenhayn it is more distinguishable as purely attrition with a coincidental presence of fortifications on the battlefield. When considering the plans of Crown Prince Wilhelm, purely concerned with taking the citadel and not with French casualty figures, it can be considered a true siege. The main fortifications were Fort Douaumont, Fort Vaux and the fortified city of Verdun itself. The Germans, through the use of a huge artillery bombardments, flamethrowers and infiltration tactics were able to capture both Vaux and Douaumont, but were never able to take the city, and eventually lost most of their gains. It was a battle that, despite the French ability to fend off the Germans, neither side won. The German losses were not worth the potential capture of the city and the French casualties were not worth holding the symbol of her defense.
The development of the armoured tank and improved infantry tactics at the end of World War I swung the pendulum back in favour of maneuver, and with the advent of Blitzkrieg in 1939, the end of traditional siege warfare was at hand. The Maginot Line would be the prime example of the failure of immobile, post-World War I fortifications. Although sieges would continue, it would be in a totally different style and on a reduced scale.
The Blitzkrieg of the Second World War truly showed that fixed fortifications are easily defeated by maneuver instead of frontal assault or long sieges. The great Maginot Line was bypassed and 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 Eben-Emael, Belgium, early in World War II).
The most important siege was the Siege of Leningrad, that lasted over 29 months, about half of the duration of the entire Second World War. Along with the Battle of Stalingrad, the Siege of Leningrad on the Eastern Front was the deadliest siege of a city in history. In the west apart from the Battle of the Atlantic the sieges were not on the same scale as those on the European Eastern front; however, there were several notable or critical sieges: the island of Malta for which the population won the George Cross, Tobruk and Monte Cassino. In the South-East Asian Theatre there was the siege of Singapore and in the Burma Campaign sieges of Myitkyina, the Admin Box and the Battle of the Tennis Court which was the high water mark for the Japanese advance into India.
The airbridge methods which were developed and used extensively in the Burma Campaign for supplying the Chindits and other units, including those in sieges such as Imphal, as well as flying the Hump into China, allowed the western powers to develop air lift expertise which would prove vital during the Cold War Berlin Blockade.
During the Vietnam War the battles of Dien Bien Phu (1954) and Khe Sanh (1968) possessed siege-like characteristics. In both cases, the Vietminh and NLF 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. However, at Khe Sanh a mere 14 years later, advances in air power allowed the United States to withstand the siege. The resistance of US forces was assisted by the PAVN and PLAF forces' decision to use the Khe Sanh siege as strategic distraction to allow their mobile warfare offensive, the first Tet offensive to unfold securely. The Siege of Khe Sanh displays typical features of modern sieges, as the defender has greater capacity to withstand siege, the attacker's main aim is to bottle operational forces, or create a strategic distraction, rather than take a siege to conclusion.
One of the complications facing police in a siege involving hostages is the Stockholm syndrome where sometimes hostages can develop a sympathetic rapport with their captors. If this helps keep them safe from harm this is considered to be a good thing, but there have been cases where hostages have tried to shield the captors during an assault or refused to co-operate with the authorities in bringing prosecutions.
The 1993 police siege on the Branch Davidian church in Waco, Texas, lasted 51 days, an atypically long police siege. Unlike traditional military sieges, police sieges tend to last for hours or days rather than weeks, months or years.
In Britain if the siege involves perpetrators who are considered by the British Government to be terrorists, then if an assault is to take place, the civilian authorities hand command and control over to the military. The threat of such an action ended the Balcombe Street Siege in 1975 but the Iranian Embassy Siege in 1980 ended in a military assault and the death of all but one of the hostage takers.