Big Ben is the nickname for the great bell of the clock at the north end of the Palace of Westminster in London, and is generally extended to refer to the clock or the clock tower as well. The clock tower holds the largest four-faced chiming clock in the world and is the third-tallest free-standing clock tower.It celebrated its 150th anniversary on 31 May 2009, during which celebratory events took place. The tower was completed on 10 April 1858 and has become one of the most prominent symbols of both London and England, often in the establishing shot of films set in the city.
The clock and dials were designed by Augustus Pugin. The clock dials are set in an iron frame 7 metres (23 ft) in diameter, supporting 312 pieces of opal glass, rather like a stained-glass window. Some of the glass pieces may be removed for inspection of the hands. The surround of the dials is gilded. At the base of each clock dial in gilt letters is the Latin inscription:The pendulum is installed within an enclosed windproof box sunk beneath the clockroom. It is 3.9m long, weighs 300 kg and beats every 2 seconds.
Along with the Great Bell, the belfry houses four quarter bells which play the Westminster Quarters on the quarter hours. The four quarter bells are G♯, F♯, E, and B. They were cast by John Warner & Sons at their Crescent Foundry in 1857 and 1858 (E). The Foundry was in Jewin Crescent, in what is now known as The Barbican, in the City of London.The origin of the nickname Big Ben is the subject of some debate. The nickname was applied first to the Great Bell; it may have been named after Sir Benjamin Hall, who oversaw the installation of the Great Bell, or after boxing's English Heavyweight Champion Benjamin Caunt.