"Silence, please" sign
from WikipediaThe White Tower, the square building with turrets on each corner that gave it its name, is actually in the middle of a complex of several buildings along the River Thames in London, which have served as fortresses, armories, treasuries, zoos/menageries, mints, palaces, places of execution, public records offices, observatories, shelters, and prisons (particularly for upper class prisoners). This last use has led to the phrase "sent to the Tower" meaning "imprisoned".
