Under Siege – Purpose of a Castle Moat

Why did they build Castle Moats?

It is a lot of hard work to build a Castle moat, let’s be honest, useless it was a naturally formed moat!

Making a Castle Moat

So Why go to all that trouble?

A medieval castle moat was a defensive structure that surrounded a castle’s walls. It was built as a vital part of a castle’s defenses against an attacking force. The moat was essentially a deep and wide ditch that ran all along the peripheral wall of the castle.

It was either filled with water or set up with sharp wooden stakes. Consequently, any army marching upon a castle first had to contend with this formidable type of defense before gaining access to the castle walls.

Example of a Dry Moat at Dourdan Castle Moats

As the enemy attempted to swim through the water or ride through the wooden stakes, the defenders on the castle walls would rain down missiles and pick off many of them before they could reach castle walls.

Medieval Castle Moat Attack

Medieval Castle surrounded by water being attacked by boats


Defensive Purpose of Medieval Castle Moat

The primary purpose of a medieval castle moat was to defend the castle from any attackers. The moat served this purpose excellently by nullifying many conventional modes of attacking a castle.

By putting a huge ditch between the castle and the enemy, the moat first stopped the direct assault of the enemy.

Sully Castle Moat and Tower

As the enemy attempted to cross the moat, the castle defenders could take advantage of their superior position and rain down arrows and other missiles.

Since the moat was typically accompanied by a drawbridge, the only way for an attacker to gain access was to scale the walls, and a moat made it almost impossible for the enemy to do so by using conventional means such as scaling ladders.

drawbridge 1

Evolution of Medieval Castle Moat

The use of moats can be dated back to ancient civilizations in Egypt and elsewhere.

In the medieval period, however, the use of moats as defensive structures for castles was ‘popularized by the Normans’. Normans were descendants of Vikings who settled in Normandy in northern France in the 9th and 10th centuries.

Norman Clothing


They then invaded England in 1066 and went on to cement their control on this new territory by building motte-and-bailey castles.

It was in the construction of these castles that the Normans frequently used moat-like ditches to protect the boundaries of their castles.

Medieval Norman Castle Medieval Times

Norman Castle

By the 12th century, these rudimentary moats had evolved into proper moats which were used to protect medieval castles. The use of such moats became particularly common during the reign of Plantagenet monarchs in England.

Bodiam Castle in medieval England

Bodiam Castle

Medieval Castle Moat Construction

A medieval castle moat was constructed by digging a huge ditch around a castle. The ditch was deep and wide enough to make it impossible for an attacking enemy to cross it without barges or having to swim across the water.

Example of a Dry Moat at Dourdan Castle

As a result, the castle was preferably situated near a water body that could be used to fill up the moat whenever needed. A small dam was also typically built to manipulate water from the main body to the moat.

Overcoming a Castle Moat Caerlaverock Castle

In some cases, the moat wasn’t filled with water and was rather set up with wooden stakes. This was equally effective a defense since it made it impossible for the approaching enemy to directly cross the moat and scale castle walls.

Medieval Castle Moat - Medieval Castle Parts

Imagine how hard it would have been to overcome this medieval Castle moat