Castles in The United Kingdom - 13th–14th Centuries - Military Developments

Military Developments

Castle design in Britain continued to change towards the end of the 12th century. After Henry II mottes ceased to be built in most of England, although they continued to be erected in Wales and along the Marches. Square keeps remained common across much of England in contrast to the circular keeps increasingly prevailing in France; in the Marches, however, circular keep designs became more popular. Castles began to take on a more regular, enclosed shape, ideally quadrilateral or at least polygonal in design, especially in the more prosperous south. Flanking towers, initially square and latterly curved, were introduced along the walls and gatehouses began to grow in size and complexity, with portcullises being introduced for the first time. Castles such as Dover and the Tower of London were expanded in a concentric design in what Cathcart King has labelled the early development of "scientific fortification".

The developments spread to Anglo-Norman possessions in Ireland where this English style of castles dominated throughout the 13th century, although the deteriorating Irish economy of the 14th century brought this wave of building to an end. In Scotland Alexander II and Alexander III undertook a number of castle building projects in the modern style, although Alexander III's early death sparked conflict in Scotland and English intervention under Edward I in 1296. In the ensuing wars of Scottish Independence castle building in Scotland altered path, turning away from building larger, more conventional castles with curtain walls. The Scots instead adopted the policy of slighting, or deliberately destroying, castles captured in Scotland from the English to prevent their re-use in subsequent invasions – most of the new Scottish castles built by nobles were of the tower house design; the few larger castles built in Scotland were typically royal castles, built by the Scottish kings.

Some of these changes were driven by developments in military technology. Before 1190 mining was used rarely and the siege engines of the time were largely incapable of damaging the thicker castle walls. The introduction of the trebuchet began to change this situation; it was able to throw much heavier balls, with remarkable accuracy, and reconstructed devices have been shown to be able to knock holes in walls. Trebuchets were first recorded in England in 1217, and were probably used the year before as well. Richard I used them in his sieges during the Third Crusade and appears to have started to alter his castle designs to accommodate the new technology on his return to Europe. The trebuchet seems to have encouraged the shift towards round and polygonal towers and curved walls. In addition to having fewer or no dead zones, and being easier to defend against mining, these castle designs were also much less easy to attack with trebuchets as the curved surfaces could deflect some of the force of the shot.

Castles saw an increasing use of arrowslits by the 13th century, especially in England, almost certainly linked to the introduction of crossbows. These arrowslits were combined with firing positions from the tops of the towers, initially protected by wooden hoarding until stone machicolations were introduced in England in the late 13th century. The crossbow was an important military advance on the older short bow and was the favoured weapon by the time of Richard I; many crossbows and vast numbers of quarrels were needed to supply royal forces, in turn requiring larger scale iron production. In England, crossbows were primarily made at the Tower of London but St Briavels Castle, with the local Forest of Dean available to provide raw materials, became the national centre for quarrel manufacture. In Scotland, Edinburgh Castle became the centre for the production of bows, crossbows and siege engines for the king.

One result of this was that English castle sieges grew in complexity and scale. During the First Barons' War from 1215 to 1217, the prominent sieges of Dover and Windsor Castle showed the ability of more modern designs to withstand attack; King John's successful siege of Rochester required an elaborate and sophisticated assault, reportedly costing around 60,000 marks, or £40,000. The siege of Bedford Castle in 1224 required Henry III to bring siege engines, engineers, crossbow bolts, equipment and labourers from across all of England. The Siege of Kenilworth Castle in 1266, during the Second Barons' War, was larger and longer still. Extensive water defences withstood the attack of the future Edward I, despite the prince targeting the weaker parts of the castle walls, employing huge siege towers and attempting a night attack using barges brought from Chester. The costs of the siege exhausted the revenues of ten English counties. Sieges in Scotland were initially smaller in scale, with the first recorded such event being the 1230 siege of Rothesay Castle where the besieging Norwegians were able to break down the relatively weak stone walls with axes after only three days. When Edward I invaded Scotland he brought with him the siege capabilities which had evolved south of the border: Edinburgh Castle fell within three days, and Roxburgh, Jedburgh, Dunbar, Stirling, Lanark and Dumbarton castles surrendered to the king. Subsequent English sieges, such as the attacks on Bothwell and Stirling, again used considerable resources including giant siege engines and extensive teams of miners and masons.