In the first instance, when the interest of the king and of his barons
was identical, the former had only retained in his hands the castles in
the chief towns of the shires, which were entrusted to his sheriffs or
constables. But the great feudal revolts under the Conqueror and his
sons showed how formidable an obstacle to the rule of the king was the
existence of such fortresses in private hands, while the people hated
them from the first for the oppressions connected with their erection
and maintenance. It was, therefore, the settled policy of the crown to
strengthen the royal castles and increase their number, while jealously
keeping in check those of the barons. But in the struggle between
Stephen and the empress Maud for the crown, which became largely a war
of sieges, the royal power was relaxed and there was an outburst of
castle-building, without permission, by the barons. These in many cases
acted as petty sovereigns, and such was their tyranny that the native
chronicler describes the castles as "filled with devils and evil men."
These excesses paved the way for the pacification at the close of the
reign, when it was provided that all unauthorized castles constructed
during its course should be destroyed. Henry II., in spite of his power,
was warned by the great revolt against him that he must still rely on
castles, and the massive keeps of Newcastle and of Dover date from this
period.
[Illustration: From Clark's _Med. Mil. Arch._