Since Greek and Roman times, man has strived to establish some type of a fortification for protection and shelter. Over the pursuing centuries these evolved into a form of military and residential places known as castles.
When William the Conqueror, conquered England in 1066, his armies quickly erected wooden palisades (a fence of stakes or iron railings forming an enclosure or defence) establishing a presence in the former Saxon kingdoms. Many of these fortresses were constructed on sites that had previously been fortified in pre-Roman times, then by the Romans themselves and lastly by the Saxons who established the first kingdoms there.
As times became less turbulent and settled, the Normans became integrated into every day life and were eventually accepted by the local populace. These wooden palisades slowly began to disappear, to be replaced with stone. Any new fortifications built from that time onward were constructed entirely from stone.