It is one of the most famous landmarks in England.
The name Big Ben originally referred to just the bell but now it encompasses the clock, the tower and the bell.
Big Ben chimes on the hour and has quarter bells that chime every fifteen minutes.
Tours are available to only UK residents by request through a Member of Parliament or a Member of the House of Lords.
Visitors go through airport style security checks.
The area is surveilled using CCTV cameras, alarms, and other security technology.
1843 - Construction on the clock tower begins.
February 1852 - Clockmaker Edward John Dent is recruited to design the clock.
1853 - Dent passes away. His stepson, Frederick Dent takes over the project.
1856-1857 - The bell is cast in northern England and transported to London. It develops a crack and a replacement bell is cast.
April 10, 1858 - The replacement bell, 2.5 tons lighter than the original, is cast or molded.
1859 - Construction on the tower is complete.
May 1859 - The clock begins keeping time.
July 11, 1859 - Big Ben chimes for the first time.
September 1859 - Big Ben's great bell cracks two months after its first chime and is taken out of commission. A smaller quarter bell chimes on the hour for four years. In 1863, the great bell is turned so an undamaged portion is struck with a smaller hammer.
1923 - Big Ben's chimes are broadcast by BBC Radio on New Year's Eve.
1939-April 1945 - The clock dials are unlit due to wartime blackout regulations.
August 1976 - Nine months of repairs begin.
2007 - Big Ben is silent for seven weeks as repairs are made on the clock.
2009 - Special events all year mark Big Ben's 150th anniversary.
2011 - It becomes apparent that Big Ben has started to lean to one side. It is estimated that there is a change of less than one millimeter per year.
September 12, 2012 - Big Ben's Tower is renamed Elizabeth Tower in honor of Queen Elizabeth II's Diamond Jubilee, her 60th anniversary on the throne.
October 2015 - The British newspapers, the Mail on Sunday and Sunday Times report that the clock is in need of repair. A parliamentary report notes that Big Ben may stop working or the clock's hands could fall off