The Concentric castle was developed in the 12th and 13th centuries and offered the best protection against attack.
The word concentric means one circle inside another (this referred to the walls of this type of castle).
Concentric Castles can be described as "a Castle within a Castle". They had two or three walls around the keep. (N.B. some concentric castles didn't have a keep. Instead, inside the outer wall, there was another wall connecting a series of towers.)
The inside walls were built higher than the outside walls. This meant that defenders could fire arrows over the heads of the soldiers defending the outside walls.
Krak des Chevaliers: a concentric castle
Dover Castle in Kent UK was one of the first castles where the idea of a cocentric castle was tried out by Henry III. He also put an outer wall around the Tower of London making that a concentric castle.
Dover Castle - stands at the heart of a concentric ring of defences.
The first in western Europe to be built to a concentric design.
Having many walls meant that even if an enemy broke through the outer wall, there was, in effect, a second castle securely defended and stored with provisions.
The space between the two walls was known as the 'death hole' for being trapped within the walls would almost certainly result in death for the attacker.
Some Concentric castle had a moat for additional protection.
Considered to be the best example of a concentric castle.
Concentric castles became even more popular after the invention of gunpowder since they could withstand a siege whilst a regular castle could not.