The principle was to funnel assaulting forces into attacking a very narrow front and focusing all of the castle's defences in that area. This would mean that both architectural devices and manpower could be concentrated, unlike the more familiar concentric castle, for which the entire circumference needed to be defended.
Linear castles tended to be built where geography favoured this approach. The Knights Hospitaller fortress of Margat in Syria is built on a narrow rocky promontory, ideal for preventing successful undermining but inappropriate for the rings of walls needed for a concentric castle. The core of Krak des Chevaliers is located in a narrow gully carved from sheer rock walls severely limiting possibilities for a flank attack.
The theory of linear castles arrived in Britain in the mid thirteenth century, so the concept co-existed with concentric castles. The earliest recognised linear castle in Britain is at Tintagel, having a series of defensive wards in a row. Conway and Caernarvon Castles were both built in a linear style, defending a peninsula.
It is also worth noting that many castles naturally combined elements of both concentricity and linearity. Conwy Castle, often cited as a concentric castle, is really a linear castle with concentric elements bolted on.
- Linear castles, BBC
- Jane Eastoe, Anny Kilbourne (2007), Britain's Best: The Nation's Favourite Historic Places, Pavilion Books
- Tintagel Castle, Engineering Timeslines, archived from the original on 2012-03-07
- Philip Warner (2001) , The Medieval Castle: Life in a Fortress in Peace and War, Penguin Books, p. 142