Johnston R.A. All Things Medieval: An Encyclopedia of the Medieval World

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Sieges

In ancient times, cities often had strong walls around them, and warfare

against these cities had always involved the basic tasks of breaking the walls,

going over or under the walls, or starving the defenders into surrender.

In the Middle Ages, Europe’s decentralized political structure put a new

twist on the siege by planting heavily fortiﬁ ed castles all over the landscape.

Constantinople’s thick city walls were similar to the fortresses of Roman,

Greek, and more ancient times. Northern Europe, on the other hand, had

several hundred small fortresses that were designed to hold off dispropor-

tionately larger attackers. In order to capture a region, an invader would

need to besiege more than one fortress.

After the period of the First Crusade, knights returned with much

grander ideas of defensive fortiﬁ cation. They had seen Byzantine fortress

designs and had participated in attacks on Antioch, Acre, Jerusalem, and

Tyre. Crusaders had built their own fortresses to hold the new territory,

and they had used local engineering and labor to build much larger stone

fortresses than Europe had at the time. When they came home, many re-

built their family castles to incorporate the new defensive features. Castles

became harder to capture by direct assault.

Sieges, attacks that stretched out over a long period of time, were the

only way of capturing a castle unless it was taken by surprise. Sieges were

expensive for both sides. The attackers had to sustain an army in hostile ter-

ritory for a number of months, while the defenders had to make their food

and water last. Both sides worked hard to attack or defend the walls. Walls

could be broken down or surmounted by going over or under the walls.

Siege machinery falls into three basic types. Catapults threw projectiles over

the castle walls, either into the castle or from the castle toward the attack-

ers. Rams battered the walls to make them fall down. Siege towers lifted

attackers to the top of the wall so that they could enter.

Because of the high stakes and expense, sieges were not governed by the

polite rules of chivalry. No trick was too dirty, gross, or savage. Treachery

was one of the best ways of breaking a siege, if an insider could be bribed to

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open the gates or tell of a secret weak point. Poison or bacterial contamina-

tion of food or water was a popular way to break a siege.

Climbing, Ramming, and Digging

The simplest siege weapon was the ladder. The attackers wanted to get

into the fortress, and one way was to go over the walls. Siege ladders had

been used against city and fortress walls since ancient times. Basic facts that

governed the construction of siege ladders began with length: if a ladder

was too short, it would not allow the attacker to go over the top, but if it

was too long, its top would stick up where defenders could shove it away.

The ladder had to lean enough to be stable, but it had to be vertical enough

to be strong. The ideal siege ladder came to just below the top of the wall,

and its foot was placed at a distance from the wall equal to about half its

length. Since the walls of a town or castle were of varying heights, and were

surrounded by varying terrain, the attackers had to build custom siege lad-

ders for each position.

A reﬁ nement on the simple ladder was a ladder with a bridge. The bridge

was a sturdy plank hinged at the top of the ladder, raised by ropes. The lad-

der had to be somewhat freestanding, like a platform, since it could not

lean against the wall. Some engineers designed folding ladders that could

be made in advance and carried with the army or ladders that could be as-

sembled from short sections. Some sieges also used ladders made of rope or

leather, with hooks at the top. These ladders were for quiet night attacks,

when the ladders could suddenly appear hooked on top of the walls by long

poles without the defenders having seen any ladders.

Defenders tried to repel attackers on ladders by using the force of grav-

ity. Standing at a higher level, they could drop harmful substances on the

climbers. Most often, they threw large rocks to knock the attackers off the

ladders or force them to cover their heads. Sometimes they threw or poured

boiling water, oil, or any other hot substances they had on hand, such as

tar. They could also throw quicklime, a highly caustic, alkaline material that

burned on contact. In sandy places, they could heat sand to red-hot and

ﬂ ing it down. In some cases, they could ﬂ ing nets onto the attackers when

they reached the top and trap them.

To protect against all these defenses, attackers used heavy shields. Since

classical times, there had been siege shields made tall, curved back, or with

a small roof, and at times on wheels. Many shields were large enough for

more than one man. Medieval sieges used all forms of wooden shields, cov-

ered with leather. In the 15th century, the tall siege shield was called a pavis.

It often had a spike to drive into the ground and a pole to hold it up.

Of course, the ﬁ rst defense against siege ladders had been put in place

before the siege began, when the fortress was designed. Most fortresses

If a city or castle were not heavily defended, attackers could directly assault the walls

with ladders. Ladders were a quick way to get to the top and over the wall, but in

most sieges, the defenders were able to push the ladders back or drop stones on the

men climbing up. A slower method was to dig under the wall, assuming it was not

built on bedrock. In this scene representing a French assault on Genoa, an archer is

working to keep defenders on the run, allowing the attackers to work freely.

Normally, the city’s walls were equally crowded with archers returning ﬁ re.

(The British Library/StockphotoPro)

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used a ditch or moat that came as close as possible to the outer walls. At-

tackers had to ﬁ ll in the ditch with sacks or barrels of rocks and earth. In

some cases, they resorted to using catapults to land rocks and dirt in the

moat. Unless the ground was reasonably level approaching the wall, their

use of siege machines would be limited.

If the attackers continued to try to go over the walls, but needed more

than ladders, the next logical step was to make portable sheds. Sheds could

be made ﬁ re resistant with water and fresh skins. Sheds could also disguise

or protect structural attacks, such as digging or battering rams.

The purpose of a ram is simple. It is a strong tree trunk that hits a wall,

gate, or door repeatedly until the object is smashed. The design of a batter-

ing ram had three aims: to strengthen the ram itself, to increase its force,

and to protect its operators from counterattack.

The end of the battering ram was strengthened by a metal tip. Some-

times this was actually in the shape of a ram’s head, invoking the ram’s

butting strength and using the ram’s extended snout as the focal point of

the battering force. More often, it was a blacksmith’s iron binding so that

the wood did not shatter as easily from the force put on it. The ram’s bulk

was suspended by ropes that could swing it, so the operators of a batter-

ing ram did not need much human power to strike with it. Longer ropes,

of course, gave it more swinging power. The frame that suspended the

ram was usually roofed so that its operators were protected from arrows or

stones. Finally, the roof was often covered with damp animal skins as ﬁ re

prevention.

Defenders dropped projectiles and hot liquids on the operators of batter-

ing rams. They could also try to disrupt the action of the ram, if the ram’s

housing was too well defended to be vulnerable to rocks or ﬁ re. When the

ram struck the wall, they could try to hook it and pull it up, either deﬂ ect-

ing its blow or ﬂ ipping its shed over.

Battering ram technology had been well explored during classical times,

and, although rams were still used, castle designers built walls to withstand

them. The thickest parts of the walls were at battering level, and gates,

the main target of rams, were protected by gatehouses and moats. Attack-

ers had to ﬁ nd new ways to use rams during the Middle Ages. Small rams

could be mounted on ladders and lifted up to smash parapets. Attackers

could build an earth ramp to a higher point in a wall, where it was likely to

be thinner.

Attackers could also try to drill holes in the walls. Borers, too, had to

work in the shelter of sheds and shields. It was not easy to drill holes in

stone walls, so borers were more commonly used against brick. They were

not a large feature of Northern European siege warfare, since most French

and English castles were made of limestone and granite. A strong brick wall

could be sufﬁ ciently weakened by holes that a ram could bring it down.

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Holes could have wood pushed in and set on ﬁ re, and the heat further

weakened the walls.

By the 14th century, castle walls were built to be too high and thick for

ladders and rams to be effective. If ladders and rams could not boost attack-

ers over or batter walls down, a more elaborate machine could be built. A

siege tower was a heavy, cumbersome machine, not designed for a lightning

attack or for secrecy. It was part of an all-out assault on a weakened castle.

The tower was a tall wooden structure on wheels; it was sometimes called a

castle or a cat. It had protective walls and a roof and was ﬁ reproofed if pos-

sible. Inside, it had wooden ﬂ oors as stories where attackers could stand. A

ladder led from bottom to top, so each layer of attackers could climb the

ladder in turn. A top ﬂ oor allowed archers to give further defensive cover

to the attackers. The siege tower also had a bridge to cross to the top of

the wall. This bridge could be a drawbridge, operated by a windlass in the

bottom story.

Certain engineering issues governed the construction of siege towers.

They had to be tall enough to reach the walls and stable enough not to tip

when loaded with climbing soldiers. They also had to be portable, usually

on wheels. Medieval siege towers were as tall as 75 feet high, but they were

often shorter. Designs in medieval illustrations appear to favor a small for-

tress on a rolling platform, reached by one or more ladders. The attackers

expected a tough ﬁ ght before they could cross a bridge, and they designed

it to have walls or even a roof. Other siege towers were more like rolling

platform ladders with bridges. The builders had to think about ﬁ re, since

the most common way to defend against a siege tower was to set it on ﬁ re.

In the Byzantine region, siege towers became obsolete when it became

clear the defenders would hurl Greek ﬁ re at them. Northern Europe was

able to use siege tower tactics longer, since it was easier to defend wood

against ordinary ﬁ re. The tower could be roofed with fresh turf or newly

skinned wet hides.

Siege towers were heavy and could easily tip over. It was difﬁ cult to move

them into position from the safe distance where they had been built. The

ground had to be level, and many teams of oxen were needed to move

them. They also needed to be moved close to the walls, which normally

meant that pushing, not pulling, force was required. One way to move a

very heavy siege platform was to sink one or more posts into the ground by

the castle walls and loop heavy pulleys and ropes around them. The plat-

form was then attached to the ropes, and it could be moved forward by

oxen walking away from the battle. The siege tower inched closer to the

fortress walls, but the muscle power moving it only moved farther out of

range. The tower could come right up to the pulleys, if the defenders had

not disrupted them. Towers could also be moved with levers, but, in any

case, they moved very slowly because of their great weight.

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Undermining a wall could be the most successful attack, and there were

fewer ways for the defenders to work against it. Ideally, the defenders would

not know that sappers were digging a tunnel under the walls. The ﬁ rst

somewhat successful underground attack in medieval times was carried out

by the Vikings when they besieged Paris in 885. After the Norman con-

quest of England, mining was part of many sieges. The siege of Rochester

Castle in 1215, when King John of England was putting down a rebel-

lion, was one of the few times when mining was a key factor in the castle’s

surrender. Miners dug under two outer walls so that the defenders were

trapped in the keep. Château-Gaillard, built by King Richard I of England,

was designed to be impregnable, but miners collapsed its walls twice. Min-

ing was a large part of Crusader warfare, on both sides.

The best location to begin a sapping operation was in a place where

the defenders could not observe what was going on without leaving the

fortress. Sappers sometimes needed to start some distance away, on the

other side of a hill. The attackers could put up a wooden palisade so that

the defenders could not see what they were doing on the other side. If the

One of the oldest methods of carrying out an attack on high walls was the siege

tower. The siege tower had to act as a covered ladder that also defended its passengers

from ﬁ re. When it had been moved close enough to the wall, the siege tower dropped

a drawbridge and the attack began. (Duncan Walker/iStockPhoto)

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diggers had to start in a place where the defenders could observe them,

they needed a strong shed to protect them. The shed was sometimes nick-

named a “tortoise” or a “sow.”

An attacking army drafted industrial miners to dig their siege tunnels.

Since stone was tunneled from deep underground, even from under the city

of Paris, miners knew how to dig any length of tunnel required, through

any materials. Beginning in a safe place, they dug underground and moved

in a carefully planned direction toward the walls. Sometimes, two tunnels

were dug as parallel galleries. As the miners tunneled, they shored up the

walls of the mine with strong timbers. Mining was an operation that re-

quired a large number of laborers, which made it difﬁ cult to carry out deep

in hostile territory.

When a tunnel successfully reached a point under the defensive wall, the

miners nearly always started a ﬁ re. The intense heat caused the ground to

expand, which cracked the walls and collapsed the tunnel. Added to the

wood carried into the tunnel, oil and fat made the ﬁ re burn hotter; one

mine ﬁ re, in the siege of Rochester, used 40 pigs as sources of fat. The

wood props securing the tunnels also burned, allowing the tunnels to col-

lapse faster.

Once gunpowder was in use, it was even easier to produce a hot blast.

It was harder to get away safely, since the combustion happened so quickly

and the blast collapsed the tunnel. The best way was to approach the wall

with snake-like curves and then use the curved passages to set a long fuse,

out of sight and reach of the blast. As the ﬁ re crept along the fuse, the min-

ers could escape out the end of the tunnel. Since gunpowder came into use

at the end of the Middle Ages, it did not become a major force in siege min-

ing until the Renaissance period.

Most walls collapsed when the ground supporting them caved in. There

were few ways to build walls that were not vulnerable to sapping. One way

was to reinforce the walls with stone columns laid like pegs through holes

in the building stones. Places with ruined Roman or Greek columns could

use them this way, but most places did not have ruined columns. The for-

tress design could also use very deep digging to place a moat or a wall in

vulnerable places.

Defenders tried to detect tunnel digging when they could not see it. A

bowl of water, set over an area being mined, quivered with the vibrations

of the tools. If they could tell where the miners were approaching the wall,

the defenders could dig down to meet and surprise them with combat.

They could sink a hole nearby and try to set the attacking tunnel on ﬁ re,

or they could ﬂ ood it if they had a moat or river inside the walls. The attack-

ers tried to make their tunneling less predictable by making decoy tunnels

or by making the tunnels take unexpected paths. Tunnels could branch out,

or they could zigzag or curve.

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Ballistic Machines

Machines that threw projectiles were known by many names in their

time, although today we refer to them all as catapults. There are a few sim-

ple forces that can provide ballistic power without explosives or motors.

Levers and gravity can be harnessed to provide ﬂ inging power. The power

of both tension and torsion derive from a material being bent so that it will

spring or unwind back to its original state.

Tension engines worked by bending wood; it would spring back to shape

when the tension was released, thus ﬂ inging a projectile with the force of

its movement. Crossbows and longbows work on this principle, and some

larger forms of crossbows could act as siege weapons, throwing larger pro-

jectiles. These great crossbows were built on a frame and used a windlass

at the back of the frame to wind the bolt on its string far back. When the

windlass was released, the wooden bow’s tension thrust its heavy bolt for-

ward with speed and great force. But wood’s ability to bend and snap back

is limited by its tendency to crack. Wooden bows could not throw anything

larger than a bolt and could not take aim at walls, but only at people.

Torsion is the force exerted by a rope that has been twisted tightly and

tries to untwist. It is the principle of a child’s toy boat or airplane that uses

a rubber band wound up tight to drive paddles or propellers as it unwinds.

Torsion had been used to drive throwing machines since ancient times. The

Romans had a throwing machine called an “onager,” a wild donkey. It used

a very thick band of rope, highly resistant to being twisted, as the torsion

spring. When a lever was inserted into the torsion spring and cranked back

so that the rope was forced to twist, on release it sprang into the air. The

lever had a sling on the end with a heavy stone. As it sprang into the air, it

struck a bar that stopped its movement, and the stone ﬂ ew out of the sling.

The onager’s simple torsion spring provided great velocity and force.

Medieval uses of the torsion spring are not as clear. There is evidence

that torsion machines of this kind were known in the time of Charlemagne.

Artists’ illustrations show a machine similar to the Roman onager, but in-

stead of a sling at the end of the lever, there is a spoon-shaped cup for the

rock to be placed in. It was probably called a mangonel. Turkish medieval

sources picture a device similar to the Roman one, called a manjaniq, used

by Muslim armies.

In the 14th century, there were large crossbows that did not use bent

wood, but rather had two separate arms with torsion springs. Different

types were known variously as ballistae and espringals (and in other lan-

guages, springarda or springolf ). They were more often used by a fortress’s

defenders, since they shot bolts at individuals, rather than rocks at walls.

The espringal was built into a wooden frame, mounted on a tower. On each

side, the frame had a torsion spring made of very thick horsehair rope that

was resistant to twisting. Levers inserted into each spring were pulled back

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by ropes attached to the ﬁ ring mechanism. The espringal’s ﬁ ring system

was like a crossbow, with a long groove for a bolt. The operator cranked

the bolt back, pulling on the levers and the torsion springs. Released, the

torsion springs untwisted and the levers shot the bolt forward, through the

groove and out toward the target. The bolts were long and heavy. They

could be expected to pierce wooden shields, steel armor, and sometimes

more than one body.

The third type of throwing machine used levers and gravity. Since an-

cient times, people had known that if a lever is put over a fulcrum, like a

seesaw, and the lengths are not equal, it takes a much heavier weight on the

short end to balance a lighter weight on the long end. If the short end is

suddenly weighted, the long end will ﬂ y into the air very fast. Unlike ten-

sion and torsion, which depend on the strength of bent wood or twisted

rope, lever-based machines can throw very heavy objects with relative ease.

As long as the lever’s arm and the stand with the fulcrum hinge are strong

enough, there is no load limit.

The perrier used only the lever to ﬂ ing large stones. The perrier de-

pended on a sudden downward pull by men or horses. Its frame lifted the

lever’s short arm above the men’s heads, with a rope dangling down, and

the long end rested on the ground with a sling. They could load a heavy

rock into the sling. When the payload was in place, men with ropes pulled

the short end down, as hard as they could, and the long arm with its rope

swung upward suddenly, ﬂ inging the projectile into the air. In order to

achieve signiﬁ cant force, the pull had to be both sudden and hard. Many

ropes attached to a bar allowed many men or horses to pull. Sudden pull

could be achieved by having the throwing arm restrained by a latch as the

men began pulling, so the latch could suddenly be released. The perrier

may have been in use by the 11th century.

The trebuchet used a lever with a very heavy counterweight on its short

end. The long arm, with a sling on the end, was winched to the ground,

forcing the boxy counterweight to lift into the air. Men loaded a large stone

into the sling as the long end was held down ﬁ rmly. When the long arm was

released, the counterweight fell to the ground, suddenly lifting the long

throwing arm and releasing its sling-propelled payload into the air. Because

the machine’s power depended on gravity to pull the counterweight down,

not on men or horses to tug it hard, the trebuchet was the strongest of the

throwing machines.

Trebuchets could be built larger and stronger to throw ever-larger pay-

loads. Instead of a windlass, the winching could be accomplished by one or

two wheels, the way the tallest cranes raised loads. Several men stood inside

the wheel and walked on its steps, using their weight and a pulley system

to magnify the force. The counterweight, perhaps by now a large wooden

bucket ﬁ lled with many large stones, slowly lifted into the air. The throwing

A wall painting shows an elegant view of a castle siege using a trebuchet. Just as

the defenders are out of proportion to the size of the castle, the trebuchet shown

is far too delicate to handle the real work of a catapult. The artist has captured

the basic essence of a trebuchet, though: a weight (shown as a square against the

dark diapering design of the wall) will suddenly drop, and this momentum will

ﬂ ing the other arm into the air. The stone, shown cradled in a basket, will gain

extra force from the additional swing of its rope. A succession of stones might

succeed in damaging the wall sufﬁ ciently to pull it down. (The British Library/

StockphotoPro)