 Behind the Horseshoe Cloister is the Curfew Tower , one of the oldest surviving parts of the Lower Ward and dating from the 13th century . The interior of the tower contains a former dungeon , and the remnants of a sally port , a secret exit for the occupants in a time of siege . The upper storey contains the castle bells placed there in 1478 , and the castle clock of 1689 . The French @-@ style conical roof is a 19th @-@ century attempt by Anthony Salvin to remodel the tower in the fashion of Eugène Viollet @-@ le @-@ Duc 's recreation of Carcassonne . 
