Leonardo Da Vinci Castle

Castles were introduced into England shortly before the Norman Conquest in 1066. The motte and bailey remained the dominant form of castle in England, Wales, and Ireland well into the 12th century. At the same time, castle architecture in mainland Europe became more sophisticated. The donjon was at the centre of this change in castle architecture in the 12th century. Central towers proliferated, and typically had a square plan, with walls 3 to 4 m (9.8 to 13 ft) thick. Their decoration emulated Romanesque architecture, and sometimes incorporated double windows similar to those found in church bell towers. Donjons, which were the residence of the lord of the castle, evolved to become more spacious. The design emphasis of donjons changed to reflect a shift from functional to decorative requirements, imposing a symbol of lordly power upon the landscape. This sometimes led to compromising defence for the sake of display. Historians have interpreted the widespread presence of castles across Europe in the 11th and 12th centuries as evidence that warfare was common, and usually between local lords.
In some countries, before a castle could be built it was necessary to obtain the permission of the king through a licence to crenellate, or else the builder risked it being slighted – deliberately damaged to such an extent that the castle was undefendable. This was not universal as in some countries the monarch had little control over lords, or required the construction of new castles to aid in securing the land so was unconcerned about granting permission – as was the case in England after 1066 and the Holy Land during the Crusades. Switzerland is an extreme case of there being no state control over who built castles, and as a result there were 4,000 in the country. Before the 12th century, castles were as uncommon in Denmark as they had been in England before the Norman Conquest. The introduction of castles to Denmark was a reaction to attacks from Wendish pirates, and they were usually intended as coastal defences.
• Innovation and scientific design
Until the 12th century, stone-built and earth and timber castles were contemporary, but by the late 12th century the number of castles being built went into decline. This has been partly attributed to the higher cost of stone-built fortifications, and the obsolescence of timber and earthwork sites, which meant it was preferable to build in more durable stone. Although superseded by their stone successors, timber and earthwork castles were by no means useless. This is evidenced by the continual maintenance of timber castles over long periods, sometimes several centuries; Owain Glyndŵr's 11th-century timber castle at Sycharth was still in use by the start of the 15th century, its structure having been maintained for four centuries.