I found this an interesting fact:
Pre-built Norman castles were loaded on to the Norman invasion fleet in 1066. The first pre-built Norman Wooden Castle was erected at Pevensey Bay in 1066. The temporary wooden Motte and Bailey castles were quickly replaced by the permanent stone Norman castles which were dominated by their tower Keeps. The Tower of London is strongly associated with William the Conqueror who invaded England in 1066. William the Conqueror initially built a wooden Motte and Bailey castle and the famous, fortified, stone White Tower, which replaced the original Motte and Bailey castle, was completed in 1097. There were no castles in England prior to 1066. (Source: Norman Castles)