Silent Defender: How Caltrops Shaped Ancient Warfare

Dating back over 2,300 years, the caltrop, sometimes spelled caltrap, is one of the most insidious weapons ever created. Designed with four sharp spikes to ensure it had a stable base, crucially no matter how it landed one of the spikes was always pointing upwards. Laid out by the thousand on battlefields, they were designed to stop men, animals and vehicles from advancing, and they did exactly that.

In any number of ways the caltrop – called murex ferreus by the Romans, meaning ‘jagged iron’ – is the perfect weapon. They’re small and cheap to make, can be carried in their thousands, don’t need any specialist training or skills to deploy, and require no maintenance or servicing. Above all, their design has changed little in over two millennia.

Let’s take a trip back in time to discover the story of the caltrop, the silent defender.

Caltrops were used extensively in both ancient and mediaeval warfare to impede enemy movement and enhance defensive tactics.

It’s impossible to know with any degree of certainty when the caltrop was first used. Some sources suggest its first recorded use may have been during the Battle of Gaugamela between the forces of Alexander the Great and Persian King Darius III of the Achaemenid Empire in 331 BC. However, it’s certainly possible they may have been used earlier.

The Roman caltrop was used at the famous Battle of Carrhae in 53 BC fought between the Roman forces of Marcus Licinius Crassus and the Parthian armies of Surena and Silaces. Famed as one of the most brutal defeats in Roman history, writer Vegetius wrote of the caltrop’s effects on scythed chariots in De re militari –

The Roman soldiers rendered them useless chiefly by the following contrivance: at the instant the engagement began, they strewed the field of battle with caltrops, and the horses that drew the chariots, running full speed on them, were infallibly destroyed.

Caltrops were also used in other famous Roman engagements, such as the Siege of Alesia in 52 BC, where Julius Caesar’s forces used them to great effect against Gallic reinforcements.

In mediaeval warfare, caltrops became even more integral as a form of psychological as well as physical area denial. They were scattered around castles, city gates, and even during retreats to slow pursuing forces. This use was recorded during various sieges and battles where forces sought to protect strategic retreats or control the flow of battle by channelling enemy troops into more vulnerable positions.

During Japan’s feudal era between the end of the twelfth century and the beginning of the seventeenth, armies used a version of the caltrop known as the makibishi. Crafted from sharpened bamboo or iron, these devices were scattered on battlefields and potential retreat paths to slow down and injure pursuing enemies, particularly during the era of the samurai.

Makibishi played a critical role in guerrilla warfare tactics and castle sieges, offering a passive yet effective means of controlling enemy movement and securing tactical advantages.

The term caltrop derives from the Old English calcatrippe (heel trap), which is a testament to its designed purpose – to maim and slow enemies stealthily. The French used a similar word chausse-trape, or shoe-trap.

The Latin word for the caltrop is tribulus, and today, it’s the scientific name of the plant known as the caltrop – tribulus terrestris – which has spiked seed cases that are exceptionally painful if they’re stood on and in some cases, are so sharp they have been known to puncture bicycle tyres.

For reasons unknown, the caltrop went in and out of fashion over the centuries, perhaps due to the proliferation of gunpowder-based weapons like cannons, muskets and rifles. However, they became popular again in the twentieth century.

In World War I, as trench warfare dominated the European landscape, caltrops were used to impede enemy infantry movements. They were strategically placed in no-man’s land – the deadly territory between opposing trenches – to slow down or injure soldiers attempting to cross during attacks or raids.

World War II saw a further evolution in the use of the caltrop with the introduction of larger versions designed to deflate tyres and even stand in the way of vehicles, by then the backbone of military logistics and mechanised brigades. Known variously as road caltrops or caltrop obstacles, these larger devices were used to defend against the rapid advances of motorised enemy forces, particularly during retreats or defensive operations. The bigger versions, known colloquially as ‘Czech Hedgehogs’ were deployed by the Germans on the beaches of Normandy in an attempt to stop the D-Day landings. They were part of a broader set of obstacles, including tank traps and barbed wire, used to slow down the enemy and inflict maximum disruption on their mobility.

This adaptation highlights their continued relevance and versatility in changing combat environments, from countering human and horse mobility to confronting modern mechanical warfare on land and sea.

Today, a modern development of the caltrop is often used by the police to stop speeding cars. They’re known as ‘stingers’ or ‘tyre deflation devices’ and they’re laid across the width of a road on a track to instantly puncture a car’s tyres.

The tribulus stands as a testament to the enduring ingenuity of ancient military engineers and strategists. Its simplicity belied a lethal efficiency that enabled it to shape the course of battles across centuries, from the sweltering expanses of Asia and the Middle East traversed by Alexander the Great to the freezing muddy trenches of northern France in World War I.