5 Important Roman Siege Engines

Colin Ricketts

5 mins

24 Jul 2018

Almost as soon as mankind started to gather together in the settlements that facilitated civilisation (a word derived from civitas meaning city), he started to build defensive walls around them.

Cities provided rich pickings for attackers and soon became symbolic rallying points for whole cultures. Military victory often meant the taking of a capital city.

Rome hid behind its own Aurelian walls, some of which still stand today. The wall the Romans built around London was part of our capital’s defence until the 18th century.

The Romans were also masters of smashing down any defences that got in their way. Forget siege as a passive process of starving out an enemy, the Romans were more proactive than that, armed with a plethora of impressive machines to prise open recalcitrant cities.

1. The ballista

Ballistae are older than Rome, and probably the product of Ancient Greece’s way with military mechanics. They look like giant crossbows, though a stone would often replace the bolt.

By the time the Romans were firing them, ballistae were sophisticated, accurate weapons, said to be capable of picking off single opponents, pinning a Goth to a tree according to one report.

A sliding carriage was powered forward by the release of twisted animal-sinew ropes, shooting a bolt or rock up to around 500 m. A universal joint that was invented just for this machine helped pick out the target.

carroballista-engraving-

A horse drawn carroballista shown on Trajan’s column.

Ballistae were on the ships Julius Caesar first sent ashore in his attempted invasion of Britain in 55 BC, after they had helped him subdue the Gauls. They were standard kit after that, growing in size and becoming lighter and more powerful as metal replaced wood construction.

Ballista lived on in the eastern Roman military after the fall of the Western Empire. The word lives on in our modern dictionaries as a root for “ballistics”, the science of projecting missiles.

2. The onager

Torsion also powered the onager, a precursor of medieval catapults and mangonels that still hadn’t matched their power many centuries later.

It was a simple machine. Two frames, one horizontal and one vertical, provided the base and the resistance against which the firing arm was smashed. The firing arm was pulled down to the horizontal. Twisted ropes within the frame provided the tension that was released to shoot the arm back towards the vertical, where the vertical buffer would halt its progress helping to shoot its missile forward.

They more often used a sling shot to carry their deadly payload than a cup. A simple rock would do a lot of damage to ancient walls, but missiles could be coated with burning pitch or other unpleasant surprises.

One contemporary report records bombs – “clay balls with combustible substance in them” – being fired and exploding. Ammianus Marcellinus, himself a soldier, described the onager in action. He fought against the Germanic Alamanni and the Iranian Sassanids in his 4th-century military career.

An onager is also a wild ass, which like this war machine had quite a kick.

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3. Siege towers

Height is a great advantage in warfare, and siege towers were a portable source. The Romans were masters of these technological breakthroughs that date back at least as far as the 9th century BC.

Rather than delivering soldiers to the tops of city walls, most Roman siege towers were used to allow men on the ground to work at destroying the fortifications while covering fire and shelter was provided from above.

There aren’t many records of particular Roman siege towers, but one that predates the Empire has been detailed. The Helepolis – “Taker of Cities” – used at Rhodes in 305 BC, was 135 feet high, divided into nine storeys. That tower could carry 200 soldiers, who were kept busy firing an arsenal of siege engines down on the city’s defenders. The lower levels of towers often housed battering rams to slam into the walls.

As height was the key advantage sought with siege towers, if they weren’t large enough, ramps or mounds would be built. Roman siege ramps are still visible at the site of Masada, scene of one of history’s most famous sieges in 73 or 74 BC.

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4. Battering rams

Technology doesn’t come much simpler than a ram – a log with a sharpened or toughened end – but the Romans perfected even this relatively blunt object.

The ram had an important symbolic role. Its use marked the start of a siege and once the first rim hit a city’s walls the defenders had forfeited any rights to anything other than slavery or slaughter.

battering-ram-model

A scale model of a battering ram.

There is a good description of a ram from the siege of Jotapata, in modern Israel. It was tipped with a metal ram’s head and swung from a beam rather than just carried. Sometimes the men who pulled back the ram prior to slamming it forward were further protected with a fire-proofed shelter called a testudo, like the tortoise-like shield formations of the infantry. A further refinement was a hooked chain at the tip which would remain in any hole crated and pull out further stones.

The ram was very simple and very effective. Josephus, the writer who saw the great beam swinging against the citadel of Jotapata in 67 AD wrote that some walls were felled with a single blow.

5. Mines

The under-foot explosives of modern warfare have their roots in the simple digging of tunnels to literally “undermine” enemy walls and defences.

The Romans were brilliant engineers, and with a state built almost entirely around military requirements, the skills needed to extract precious metals were also part of the besieger’s arsenal.

The principles are very simple. Tunnels were dug under targeted defences with props that could be removed – usually by burning, but sometimes with chemicals – to collapse first the tunnels and then the walls above.

If mining could be avoided it probably would be. It was a massive and slow undertaking and the Romans were famous for the speed they bought to siege warfare.

wall-undermined-siege

A wall damaged by siege miners.

A good description of mining – and countermining – at the siege of the Greek city of Ambracia in 189 BC describes the construction of a massive covered walkway with carefully concealed workings being operated around the clock with shifts of diggers. Hiding the tunnels was key. Clever defenders, using vibrating bowls of water, could locate the tunnels and flood them or fill them with smoke or even poisoned gas.