The keepless castle was the greatest of all the changes introduced in the military architecture of the 13th century. The castle without a keep was certainly known in Germany fifty years before Edward’s accession to the English throne, and in France as early as 1231.
The first example of a keepless castle in Germany is Neuleiningen, built in 1224. Frederic II’s castles were of this layout. The castle of Boulogne, finished in 1231, is one of the oldest examples of this class in France. Also, the Bastille of Paris was a castle of the same kind.
The keepless castle layout is defined by a square or oblong court surrounded by a strong wall with massive towers at the angles, and in large castles, in the curtain also. Usually this inner quadrangle is encircled with an outer quadrangle of walls and towers.
The castles of this class are not invariably concentric, as shown by those built by Edward I. at Conwy, Caernarfon, and Flint. For new sites, the keep disappears, and if an old plan was altered or enlarged, the tower took a secondary position.
The keepless castle evolution resulted in the concentric Medieval castle layout. It is supposed that the concentric style of fortifications was imported by the Crusaders, who noticed the form of fortifications of Constantinople. The city was defended by a triple wall, each ring of which was higher than the one outside it. The three successive lines of defence could also be used simultaneously, each row of defenders discharging its missiles over the heads of the next.
The Keepless Conwy Castle by JMW Turner
The Crusaders showed an outstanding ingenuity in building castles, and the concentric layout is so well illustrated by the fortress at Le Krak des Chevaliers, where the curtain of the inner ward rises high above the curtain of the outer enceinte.
Approximations to the concentric plan were known in England at an early date. The earthen defences of Berkhampstead castle are concentric, although no attempt was made to correlate them by giving the inner banks command of the outer.
Once the keepless concept was known, the old castles were adapted to the new style of fortifications with an ingenuity equal to that shown on new sites.
During the reign of Henry III., additions were made to both Dover and the Tower of London, each castle acquiring a concentric plan. The effect at Dover was to ring the imposing keep with a double wall. At London, the defences were more closely planned in harmony, and one result of the additions is that, when the buildings are examined closely, the White Tower, originally the most important part of the fortress, becomes comparatively insignificant in the overall defensive scheme, suggesting the transition to the castle without a keep. The keepless Medieval castles never entirely displaced the old keep-and-bailey type. Keeps of the old sort continued to be built till the end of the Middle Ages. Hawarden Castle has a good example of a 14th century round keep; Warkworth a most remarkable specimen of the 15th, the plan being a square tower with polygonal turrets set on each face. The old type appears to have persisted in France and Germany as well. The new castles belonging mainly to the last twenty years of the 13th century cannot be named keepless anymore, they are circular castles proper, and, from the perspective of military architecture, they are the most advanced.