Room VI · Catalogue of the engines

Siegecraft

Nine ways to take a castle, from the oldest to the one that ended castles. Most sieges were won by the cheapest of them: hunger, a bargain, or an open door.

No. 1 · Counterweight trebuchet

c. 1180–1450 in Europe and the Middle East

Counterweight trebuchet

A giant throwing arm swung by a falling box of earth or stones, the heaviest artillery before gunpowder.

A long wooden beam pivots on a tall frame. The short end carries a huge counterweight, a box filled with earth, stones or lead; the long end has a sling holding the missile. Crews winched the long end down and locked it. When released, the counterweight fell, the arm whipped up and the sling opened at the top of its swing, hurling the stone in a high arc. Because the same weight fell the same distance every time, a counterweight trebuchet could hit the same stretch of wall shot after shot.

It was huge, slow and costly: it had to be built on site by skilled carpenters, took days to assemble and fired perhaps one or two shots an hour. It was exposed to enemy engines and sorties, and its high arc made it better for smashing parapets, roofs and buildings than for breaching thick walls at their foot. Defenders answered with their own engines and with timber frames and hides to protect the wall top.

Projectile: usually 50–150 kg stones; claims of much heavier ones are uncertain
Range: roughly 150–400 m in modern estimates and reconstructions, depending on size and load
Counterweight: several tonnes on the largest machines (estimates vary widely)
Rate: about 1–2 shots an hour for big machines, by modern estimates

Edward I's giant 'Warwolf' at Stirling in 1304 is the most famous named trebuchet. Siege of Stirling Castle.

Work the model

Scale model: mangonel (traction trebuchet)

No. 2 · Mangonel (traction trebuchet)

c. 600–1300 in the Mediterranean and Europe

Mangonel (traction trebuchet)

A lighter throwing arm pulled down by a team of people on ropes, quick to build and quick to shoot.

Medieval names for siege engines are muddled: writers used 'mangonel', 'petrary' and other words loosely, and we often cannot tell which machine they meant. Many historians now use 'mangonel' for the traction trebuchet, which came from China and reached the Mediterranean by about the 6th century. Instead of a counterweight, a crew of pullers (from a handful to well over a hundred) hauled on ropes tied to the short end of the arm, flinging the sling. Older books picture the mangonel as a torsion catapult with a cup, like the Roman onager; whether such machines were still used in the Middle Ages is debated.

Human muscle gives a less consistent pull than a falling weight, so shots scattered more, and the stones were smaller. It could not batter down strong masonry, but it was cheap, fast-firing and useful against people, hoardings and parapets. It needed large, exposed crews, who were easy targets for archers on the walls.

Projectile: typically a few kg up to about 60 kg
Range: often around 80–150 m
Crew: from a handful to 250 or more pullers, depending on size

Traction trebuchets were the main stone-throwers of the First Crusade, including at Antioch in 1097–98. Siege of Antioch.

No. 3 · Ballista and springald

Roman times; springalds and great crossbows c. 1200–1400

Ballista and springald

A giant crossbow or twisted-rope engine that shot heavy bolts with great accuracy.

The Roman ballista stored energy in two skeins of twisted sinew or rope, each holding an arm; pulling back the bowstring twisted them tighter, and releasing it drove a bolt or small stone forward in a flat path. In the medieval period similar torsion bolt-throwers were called springalds, alongside very large crossbows mounted on frames. They were aimed like a gun, along a line of sight, and were used to pick off engine crews, men on the walls or anyone standing in a doorway.

Bolt-throwers could kill people but could do little to stone walls. Their torsion skeins lost strength in damp weather and had to be re-tensioned. The machines were complex to build and maintain. Defenders liked them as much as attackers, since they could be mounted on towers to shoot down at siege engines.

Projectile: heavy bolts, often 0.5–1 m long
Effective range: probably up to about 200–300 m; ancient claims of more are uncertain

Edward I's armies carried springalds on their Scottish campaigns around 1300, and royal castles such as the Tower of London kept them on their walls.

No. 4 · Battering ram

ancient to c. 1500

Battering ram

A heavy beam, often iron-capped, swung against a gate or wall under a protective roof.

A tree trunk with an iron head was hung by chains or ropes inside a wheeled shed with a sloping roof covered in wet hides against fire. Medieval writers called such sheds a 'cat' or a 'sow'. The crew swung the beam back and forth against a gate or the foot of a wall, cracking timber or loosening stones. A related tool, the bore, had a pointed head to pick stones out one by one.

A ram needed to reach the wall, so a deep ditch stopped it. Defenders lowered sacks of wool or mattresses to cushion the blows, caught the beam with hooks or forked poles, dropped heavy stones on the roof and tried to set the shed alight. A sloping batter at the wall base also kept it away from the wall itself.

Beam: one large tree trunk, often over 10 m in big examples
Crew: a few dozen men, by medieval accounts

At Jerusalem in 1099 the crusaders used a great ram to break the outer wall so their siege tower could come close.

Swing the ram

No. 5 · Siege tower

ancient to the 16th century

Siege tower

A tall wooden tower on wheels, pushed against the wall so attackers could cross straight onto the wall-walk.

Built on site from timber and covered with wet hides, a siege tower (in English often called a belfry) was taller than the enemy wall. Archers at the top swept the wall-walk clear while the tower was rolled forward on a levelled track. Once it touched, a drawbridge dropped from an upper floor and soldiers poured across. Some towers held a ram on the lowest floor.

A tower needed flat, firm ground right up to the wall, so ditches had to be filled first. It was a huge target for stone-throwers and fire arrows, and could topple on soft or uneven ground. Defenders built up their own walls higher, swung beams to push it away, or dug under its path so that it sank.

Height: usually a little above the wall, so often 10–20 m
Garrison: from tens to, by one chronicle at Kenilworth, about 200 crossbowmen

At Kenilworth in 1266 a tower said to hold 200 crossbowmen was smashed by the defenders' engines. Siege of Kenilworth.

No. 6 · Mining

ancient to the 18th century and beyond

Mining

Digging under a wall, propping the tunnel with timber, then burning the props to bring the wall down.

Miners, or sappers, started a tunnel out of sight, often under cover of a shed, and dug beneath the foundations of a tower or wall. They held up the roof with wooden props. When the chamber was large enough they packed it with brushwood and fat and set it alight. As the props burned away, the tunnel collapsed and the masonry above it cracked or fell. After about 1500, gunpowder charges replaced fire.

Mining was slow and only worked where the ground could be dug: rock, water-filled moats and marshes defeated it. Defenders listened for digging, sometimes watching bowls of water for ripples, and dug counter-mines to break into the enemy tunnel and fight underground. Round towers and thick, sloping bases made mining harder.

Pace: often only a few metres a day, depending on the ground
Rochester 1215: a royal writ ordered the fat of 40 pigs to fire the props

King John's mine brought down a corner of Rochester's great keep in 1215. Siege of Rochester Castle.

Dig the mine

No. 7 · Blockade and starvation

all periods

Blockade and starvation

Surrounding a castle and waiting until food, water or hope ran out.

The surest and cheapest way to take a strong place was often to do nothing violent at all. The besieger surrounded it with camps, ditches or small forts, cut off supplies and messengers, and waited. Defenders sometimes sent out non-fighting townspeople to make food last longer, and attackers sometimes refused to let them through. Disease spread in crowded, hungry places. Many sieges ended with an agreed surrender once a garrison saw that no relief army was coming.

Starvation took months, and a besieging army had to feed itself too, often in a land it had already stripped. Its own soldiers fell ill, deserted or went home when their service ended. A well-stocked castle with a good well could outlast its attackers, and a relief army could turn the besiegers into the besieged.

Typical length: weeks to many months
Kenilworth 1266: about six months, ended by hunger and disease

At Kenilworth in 1266 the garrison held off every assault but surrendered to hunger after about six months. Siege of Kenilworth.

No. 8 · Treachery and surprise

all periods

Treachery and surprise

Taking a castle by bribery, betrayal, a night climb or a door left unguarded.

A wall is only as strong as the people on it. Besiegers bribed or persuaded a guard to open a gate or let down a rope, used spies to learn where the watch was weak, or sent small parties to climb at night where no one expected them. Negotiation also counted: many castles surrendered on terms after a token resistance, especially if their lord had already submitted.

Treachery relied on luck and on someone inside being willing. Garrisons rotated watches, kept keys with trusted officers and executed suspected traitors. A plot discovered could end with the attackers trapped inside the walls.

Cost: sometimes a bribe, sometimes nothing
Antioch 1098: one tower commander let the crusaders in after a siege of about seven and a half months

Antioch fell in June 1098 when a tower commander let Bohemond's men climb in at night. Siege of Antioch.

No. 9 · Gunpowder artillery

in Europe from the 1320s; decisive from c. 1450

Gunpowder artillery

Cannon that hurled stone or iron balls at walls, eventually forcing a new kind of fortress.

The first European guns appear in the 1320s and were small. By the 15th century founders cast or forged enormous bombards that threw stone balls weighing hundreds of kilograms. Fired low and repeatedly at the same spot, they could shatter a tall, thin medieval wall. Later, lighter bronze and iron guns on wheeled carriages could be moved with an army and fired faster. Gunpowder also made mines far more powerful.

Early cannon were slow to load, inaccurate and sometimes burst, killing their crews. The largest bombards fired only a few shots a day and needed huge teams to move. Defenders replied by thickening and lowering walls, backing them with earth that absorbed shot, cutting gunports for their own cannon and, from about 1500, building angled bastions.

Largest bombard balls: several hundred kg, up to about 700 kg for the very largest; figures for 1453 vary between sources
Rate: the biggest guns: a few shots a day
First European image: an English manuscript of 1326

Ottoman cannon battered the land walls of Constantinople for seven weeks in 1453. Siege of Constantinople.