Wherever they went, William and his Norman lieutenants built castles.
About 170 great vassals came to England with William. When the
king rewarded his followers with grants of land, they also assumed the responsibility
for its defense, so each built one or more castles. William and
his men had several reasons for building castles. As hostile invaders they
had to fortify their dwellings and camps in order to hold the territory and
provide security for themselves. Their castles also secured borders and
coastlines against other invaders and controlled the movement of people
and goods at key transportation centers such as fords, bridges, and
passes and along major roads.
World History
