Since William the Conqueror built the the Original white tower around 1100 the tower of London has had may additions and served many different functions. No matter what the tower was being as: palace, prison, zoo there is no question that throughout the centuries it has been and remains a symbol of power and wonder. 

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Sources: hrp.org.uk, juliandboris.com, history.com, imdb.com, wikipedia.org, britannica.com