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Building a Castle: Curtain Wall Defences

Crenellations, mural passages, hoardings, machicolations, guttering

The curtain wall was the main defence of the castle, but it wasn’t just a wall, it contained defences of its own.


Tower of London

The most obvious are the crenellations, the up-and-down parts on top of the wall. They were named after the gaps from which bowmen could shoot, called crenels. The raised parts, providing cover for the bowmen, were called merlons. The wall walks behind the crenellations provided a high vantage point for lookouts and from which to fire on attackers.

Mural passages

Wall Passage

The walls were very thick, and in some places passages were created inside the wall of mural towers so defenders could get from one wall walk to another without having to cross the area of the fighting. They could also be used to hide people away from the attackers, wives and children for example.


Hoardings Carcassonne Castle

Some towers had wooden hoardings built on top, either permanent or hastily constructed before an attack. The hoardings would project out from the tower and had open sides which offered cover for bowmen while they attacked from a height, and could be used to drop weapons or hot sand or quicklime on the attackers below.

Some hoardings had a protective roof. There was always the danger from fire though and various methods were used to try to protect the roof from flaming arrows and firebombs. The roof was sloped to encourage the missiles to roll off, and was sometimes covered with animal skins. If an attack was imminent they could also soak the timber to try to prevent fire.


Machicolations Montealegre Castle

These are the stone equivalent of hoardings, less vulnerable to missiles and fire. They had downward-sloping holes through the wall, which were used to pour hot substances or clay pots filled with flammable liquids like tar on the attackers below.


Guttering spout

There was another danger to the walls, not from attackers but from rain. It could undermine foundations, weaken masonry, wash away joints and turn the lime within the walls to liquid. Drainage systems were therefore an important consideration in castle design.

The lowest part of the walls sloped outwards to protect the foundations, and spouts were created to allow water in the courtyard and bailey to drain away into the castle ditch. Molten lead was used to create sealing joints in the guttering stones.

[adapted from The Medieval Castle Haynes Manual by Charles Phillips]

Ann Marie Thomas is the author of four medieval history books, a surprisingly cheerful poetry collection about her 2010 stroke, and the science fiction series Flight of the Kestrel. Book one, Intruders, and book two Alien Secrets, are out now. Follow her at