A concentric castle is a much larger construction than Motte and bailey or Stone keep castles.

Concentric Castles, (see Beaumaris and Caerphilly Castles), make best use of angles in a castles design, providing the defender with more opportunity to hurt any attacking force.

Essentially a concentric castle is a series of defensive structures. The typical design, as outlined in the image below, has two curtain walls, the outer one lower than the inner one. Each of the walls has a variety of rounded towers from which a defender has a number of vantage points over his assailant. In addition to the number of curtain walls and towers the castle was, usually, surrounded by water, making attack even more perilous.

Major advantages of a Concentric Castle:

• Round towers couldn't be mined as easily.
• Larger Castles can house a greater number of defendants.
• Once inside the outer wall an attacker was still visible to defenders in a large number of towers.
• The symmetrical design ensures that entry to the inner most parts of the Castle is closely monitored.
• Low curtain walls mean that defenders on the inner and outer walls can see attackers.
• A small number of men could defend a large part of the castle.