Last updated: 13 August 2008
Linear castles were constructed when concentric castles weren't a practical option, and the Normans would build structures designed to direct the enemy's fire.
Sometimes a defence's location meant that to build a concentric castle would be impossible or militarily foolish. By definition, a concentric castle needs to be defended equally around its circumference.
A linear castle concentrated its defences on one side or point of the castle, and used its structure to focus the enemy's attention on to its best-defended area. The name comes from their structure of a series of linear barriers in front of the enemy.
Geographical location often forced the builder to choose between a concentric or linear structure - Caernarfon castle's location on a narrow rock precluded a concentric structure, and it remains one of the UK's most famous linear castle structures.