Title: List of castles in England
Content:  A castle is a type of fortified structure, developed in Europe during the Middle Ages. The first castles appeared in France in the 10th century, and in England during the 11th century. A few castles are known to have been built in England before the Normans invaded in 1066; a great many were built in the years following, the principal mechanism by means of which the Normans were able to consolidate their control over the country. Whilst a few important castles, such as the White Tower in the Tower of London, were built of stone, most early castles were motte-and-bailey castles of earthwork and timber, which could be 
Title: Castle
Content:  in the 11th and 12th centuries as evidence that warfare was common, and usually between local lords. Castles were introduced into England shortly before the Norman Conquest in 1066. 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. 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 
Title: Castles in Great Britain and Ireland
Content:  The English word "castle" derives from the Latin word castellum and is used to refer to the private fortified residence of a lord or noble. The presence of castles in Britain and Ireland dates primarily from the Norman invasion of 1066. Before the arrival of the Normans the Anglo-Saxons had built burhs, fortified structures with their origins in 9th-century Wessex. Most of these, especially in urban areas, were large enough to be best described as fortified townships rather than private dwellings and are therefore not usually classed as castles. Rural burhs were smaller and usually consisted of a wooden hall with a wall enclosing various domestic buildings along with an entrance tower called a burh-geat, which was apparently used for ceremonial purposes. Although rural burhs were relatively secure their role was primarily ceremonial and they too are not normally classed as castles. There were, however, a small number of castles which were built in England during the 1050s, probably by Norman knights in the service of Edward the Confessor. These include Hereford, Clavering, Richard's Castle and possibly Ewyas Harold Castle and Dover.
Title: Castles in Great Britain and Ireland
Content:  The earliest histories of British and Irish castles were recorded, albeit in a somewhat fragmented fashion, by John Leland in the 16th century and, by the 19th century, historical analysis of castles had become popular. Victorian historians such as George Clark and John Parker concluded that British castles had been built for the purposes of military defence, but believed that their history was pre-Conquest – concluding that the mottes across the countryside had been built by either the Romans or Celts. The study of castles by historians and archaeologists developed considerably during the 20th century. The early-20th-century historian and archaeologist Ella Armitage published a ground-breaking book in 1912, arguing convincingly that British castles were in 
Title: Castles in Great Britain and Ireland
Content:  The 15th and 16th centuries saw a small number of British castles develop into still grander structures, often drawing on the Renaissance views on architecture that were increasing in popularity on the continent. Tower keeps, large solid keeps used for private accommodation, probably inspired by those in France had started to appear in the 14th century at Dudley and Warkworth. In the 15th century the fashion spread with the creation of very expensive, French-influenced palatial castles featuring complex tower keeps at Wardour, Tattershall and Raglan Castle. In central and eastern England castles began to be built in brick, with Caister, Kirby 
Title: Castle
Content:  in the medieval period. During the First Crusade (1096–1099), the Frankish armies encountered walled settlements and forts that they indiscriminately referred to as castles, but which would not be considered as such under the modern definition.   Castles served a range of purposes, the most important of which were military, administrative, and domestic. As well as defensive structures, castles were also offensive tools which could be used as a base of operations in enemy territory. Castles were established by Norman invaders of England for both defensive purposes and to pacify the country's inhabitants. As William the Conqueror advanced through England, he fortified key positions to secure the land he had taken. Between 1066 and 1087, he established 36 castles such as Warwick Castle, which he used to 
Title: Encastellation
Content:  In Ireland, as in Britain and most of Europe, encastellation was primarily a Norman venture. The first castles were motte-and-baileys built on the expanding frontier of the English Pale and within it to control the local population, according to Gerald of Wales. Stone castles were slow to develop, appearing in the late thirteenth century.
Title: Castles in Great Britain and Ireland
Content:  influences. Ravenscraig Castle in Scotland, for example, was an early attempt in the 1460s to deploy a combination of "letter box" gun-ports and low-curved stone towers for artillery weapons. These letter box gun-ports, common in mainland Europe, rapidly spread across Scotland but were rarely used in England during the 15th century. Scotland also led the way in adopting the new caponier design for castle ditches, as constructed at Craignethan Castle. Henry VIII became concerned with the threat of French invasion during 1539 and was familiar with the more modern continental designs. He responded to the threat by building a famous sequence of forts, called the Device Forts or Henrician Castles, along the south 
Title: Encastellation
Content:  Normanisation began in England before the Conquest primarily through the Norman sojourn of Ethelred II and the influence of his Norman queen Emma. During the reign of Edward the Confessor (1042&ndash;1066), definite strides were taken in spreading Norman ideas to England. Castles were first built in England in his reign under the direction especially of his Norman marcher lord Ralph the Timid. Encastellation began in earnest under William the Conqueror in the years immediately following the Battle of Hastings. Castles of the motte-and-bailey were erected quickly all over the country to subdue the locals and prevent foreign invasions by rival claimants to the throne. Within a matter of years, England was fully castled. Most of these castles belonged to the king or one of his tenants-in-chief. The construction of numerous castles by minor lords was a feature, as in most places, of the reign of weaker kings. After the iron hand of William's sons had passed, Stephen took the throne and the Anarchy (1135&ndash;1152) of civil war which characterised his reign saw the proliferation of adulterine (unauthorised) castles: to the number of 1,115, according to one chronicler.
Title: Castles in Great Britain and Ireland
Content:  with England in the 1540s added to the level of insecurity over the rest of the century. Irish tower houses were built from the end of the 14th century onward as the countryside disintegrated into the unstable control of a large number of small lordships and Henry VI promoted their construction with financial rewards in a bid to improve security. English tower houses were built along the frontier with Scotland in a dangerous and insecure period. Secondly, and paradoxically, appears to have been the periods of relative prosperity. Contemporary historian William Camden observed of the northern English and the Scots, "there is not a man amongst them of a better 

Question: who brought the idea of castles to england?
Answer: Norman invaders.