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Medieval soldiers standing outside a castle

How to defend a medieval castle 


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You only have to look at medieval castles to imagine what tough targets they would have made for enemy troops. But what were the exact design features that protected them from fearsome attackers?

Moats and drawbridges

Moats acted as the preliminary lines of defence for medieval castles. Although commonly depicted as bodies of water, many moats were little more than excavated ditches surrounding the castle walls. Those filled with water from a nearby source, such as a spring or a lake, added an additional level of protection, making it difficult for attackers – already weighed down by armour and weapons – to wade across. Whether wet or dry, the moat made it virtually impossible to tunnel underneath the castle and attack the inhabitants from below.

Of course, no moat would be complete without a drawbridge. Attached to the castle walls by ropes and chains, a drawbridge would be raised during a siege to seal the gate and deny access to unwanted guests. This was far more functional than in the early medieval period, where simple wooden bridges were designed to be burnt in the event of a siege.

Outer curtain walls

Those valiant enough to make it across the moat were faced with the highly forbidding outer curtain wall. Surrounding the courtyards of castles, outer curtain walls were often built to imposing heights of over 30 feet and were thick enough to withstand attacks from battering rams. For example, the curtain wall of Caerphilly Castle in Wales was built to an impenetrable depth of over two metres.

When topped with an additional indented wall known as a battlement, these structures provided a sheltered walkway for soldiers to travel around the perimeter while protected from enemy fire. Although they played an important role in the early medieval era, improvements in weaponry left battlements as a mostly decorative feature during the later period.

Towers and turrets

Taking various forms over the centuries, towers were of paramount importance to a castle’s defence. During the early medieval period, towers were often rectangular, but they later evolved into round towers. These latter structures were less susceptible to mining, an act of tunnel warfare carried out by sappers who would dig trenches underneath the curtain wall, hoping to invade from beneath. Circular towers were also superior due to the increased line of sight for archers and were more resistant to projectiles.

Adding to the field of vision even further were the smaller towers known as turrets, which were mounted along the curtain walls and the castle walls themselves. Turrets were the perfect lookout point to spot the next siege and to provide cover for the soldiers defending the nearby towers.

Arrow loops

Arrow loops, also known as arrow slits, were narrow openings in a fortification’s walls and battlements through which bowmen could fire their arrows and bolts. Standing up to nine feet tall with a horizontal line at eye height, arrow slits often resembled Christian crosses. The walls supporting the arrow loops were tapered to allow for a wider field of vision for the archer whilst remaining a palm’s width on the outside, making it a nearly impossible target for the aggressor.

Believed to be created by Archimedes circa 214 BC, arrow loops had fallen out of fashion during the Norman invasion era, only to return as a permanent fixture in castle design by the 13th century. As advancements in weaponry and warfare evolved, so did the arrow loops, with the introduction of gunpowder calling for round openings in the slits to allow for firearms.


Yet another obstacle for intruders was the barbican, a fortified gateway manned by guards. Controlling access to the castle, a barbican would form part of the outer curtain or city walls, often located above the drawbridge or set in front of the castle’s gatehouse.

Referred to as ‘death traps’, many barbicans also featured a narrow, walled passageway that could be closed off by a spiked gate called a portcullis. This acted as a funnel to confine the enemy, making it easy for guards in the nearby towers to pick them off.

The Barbican Centre in London today gains its name from the Roman fortification built in this area in the late 1st century AD.

Machicolations and murder holes

Machicolations and murder holes shared a similar function: they were gaps through which a castle’s defenders could shoot arrows, throw rocks or pour scalding hot substances. Although these holes are popularly associated with the dousing of hot oil, historical evidence suggests that this wasn’t the go-to substance for castle defenders. Hot oil would have been far too expensive for common use, so instead the defenders typically dropped boiling water and caustic quicklime which blistered and blinded the invaders.

So what’s the difference between murder holes and machicolations? It was a matter of location. Murder holes were set within the ceilings of the castle’s interior structures, primarily in the entranceways. Their purpose was to allow the defenders to harm or kill those who had already made it through the castle gates.

Machicolations, on the other hand, hung off the side of the castle and curtain walls, acting as a deterrent to those who still poised to breach the perimeter. Indeed, later medieval castles, such as Bodiam Castle in East Sussex, were decked out with faux machicolations which lacked holes, but were intended to give an air of fearsome impregnability.