The White Tower

The great central keep was built by William the Conqueror and finished by his sons and successors, William Rufus and Henry I. It is 90 feet high and is of massive construction, the walls varying from 15 feet thickness at the base to almost 11 feet in the upper parts. Above the battlements rise four turrets; three of them are square, but that on the northeast is circular. This turret once contained the first royal observatory.