The most famous part of Charles Barry's design is the elegant clock tower. Originally called St. Stephen's Tower, it was soon named after the tower's largest bell, the Big Ben. A light at the top of the tower is illuminated when Parliament is sitting at night.
The name Big Ben is often used to describe the tower, the clock and the bell but the name was first given to the Great Bell.
The Elizabeth Tower was completed in 1859 and the Great Clock started on 31 May, with the Great Bell's strikes heard for the first time on 11 July and the quarter bells first chimed on 7 September.