The earliest medieval castles began to be built in Europe as early as the 9th and 10th centuries. At one hand, the construction of castles was instigated by the continuous struggle between the Muslim and Christian kingdoms in the region of Spain.
At the other hand, the fall of the Carolingian Empire in the 9th century left significant powers in the hands of lords and nobles in Western Europe. The lords took the opportunity to amass more power, build their own castles, establish feudal systems and house their personal garrisons.
It was during this period that the Normans, arriving first in Normandy and later in southern Italy and England, pioneered the construction of motte-and-bailey castles.
Normans settled in the north French region of Normandy during the 8th and 9th centuries. Franks who occupied the neighbouring regions had some skill in building rudimentary fortifications. Normans gradually borrowed their style of building and mixed in their own design ideas to give birth to the motte-and-bailey castles. These were the earliest types of castles which gained currency in Western Europe, most notable in all such regions which the Normans conquered.
Motte-and-bailey castles were first extensively constructed by the Normans in Normandy. When the Normans launched an invasion of Anglo-Saxon England in 1066, they came armed with the ability to erect motte-and-bailey castles in no time to defend their territories.
This skill was crucial in helping them establish their hold over the newly conquered England. Despite their conclusive success against the Anglo-Saxon king and the main army, the Normans faced stiff resistance. They were able to subdue this resistance by establishing their hold over different regions piece-meal, thanks largely to their prowess in building castles.
Motte-and-bailey castles were very easy to construct with the help of a sizable labour force, were highly effective in military terms and were fairly secure. They typically comprised of a motte situated on top of a mound of earth, comprising of the keep and the residence of the lord. This was the heart of the castle and being on a steep height, it was a very defensible structure.
The motte was also frequently surrounded by a ditch. Connected to the motte through stairs was a bailey located on ground level. The bailey housed other parts of a castle including the garrison, the stables, stores and the residential quarters of the knights as well as the peasants. The bailey was surrounded by barbicans or another effective defensive structures.
During the 11th century Norman invasion of England, the early motte-and-bailey medieval castles were highly effective. They proved vital in permanently establishing the Normans in England. However, they had a serious drawback of being wooden, mostly made of timber, and thus werer very prone to catching fire accidentally or at the hands of an attacking force. As a result, by 12th century these early medieval castles had begun to be replaced by more durable castles such as those made of stone.