The Clock Tower is the world's largest four-faced,
chiming clock. The structure is situated at
the north-eastern end of the Houses of Parliament
building in Westminster, London. It is almost
universally called "Big Ben" —
which is actually the main bell housed within
the Clock Tower. The Clock Tower has also
been referred to as The Tower of Big Ben,
Big Tom and, incorrectly, St Stephen's Tower
which is actually towards the middle of the
Palace, and is the main point of entry for
attendees of debates and committees.
The tower was raised as a part of Charles
Barry's design for a new palace, after the
old Palace of Westminster was destroyed
by fire on the night of 22 October 1834.
However, although Barry was the chief architect
of the palace, he turned to Augustus Pugin
for the design of the clock tower, which
resembles earlier Pugin designs, including
one for Scarisbrick Hall. The design for
Big Ben was, in fact, Pugin's last design
before his final descent into madness and
death, and Pugin himself wrote, at the time
of Barry's last visit to him to collect
the drawings: "I never worked so hard
in my life for Mr Barry for tomorrow I render
all the designs for finishing his bell tower
& it is beautiful" (Rosemary Hill,
God's Architect: Pugin & the Building
of Romantic Britain (2007) p 482). The tower
is designed in Pugin's celebrated Gothic
revival style, and is 96.3 metres (315.9
The first 61 metres (200 ft) of the structure
is the Clock Tower, consisting of brickwork
with stone cladding; the remainder of the
tower's height is a framed spire of cast
iron. The tower is founded on a 15 metres
(49 ft) square raft, made of 3 metres (10
ft) thick concrete, at a depth of 7 metres
(23 ft) below ground level. The four clock
faces are 55 metres (180 ft) above ground.
The interior volume of the tower is 4,650
cubic metres (164,200 cubic feet).
Due to ground conditions present since
construction, the tower leans slightly to
the north-west, by roughly 220 millimetres
(8.66 in) at the clock face, giving an inclination
of approximately 1/250. Due to thermal effects
it oscillates annually by a few millimetres
east and west.
The clock faces are large enough to have
once allowed the Clock Tower to be the largest
four-faced clock in the world, but have
since been outdone by the Allen-Bradley
Clock Tower in Milwaukee, Wisconsin. The
builders of the Allen-Bradley Clock Tower
did not add chimes to the clock, so the
Great Clock of Westminster still holds the
title of the "world's largest four-faced
chiming clock." The clock mechanism
itself was completed by 1854, but the tower
was not fully constructed until four years
later in 1858.
The clock and dials were designed by Augustus
Pugin. The clock faces are set in an iron
framework 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 heavily gilded. At the base of each clock
face in gilt letters is the Latin inscription:
"DOMINE SALVAM FAC REGINAM NOSTRAM
VICTORIAM PRIMAM", which means 'O Lord,
keep safe our Queen Victoria the First'.
The clock became operational on 7 September
During World War II, the Palace of Westminster
was hit by German bombing, destroying the
Victorian House of Commons and causing damage
to two of the clockfaces as well as sections
of the tower's steeped roof.
The Great Bell
The main bell, officially known as the
Great Bell, is the largest bell in the tower
and part of the Great Clock of Westminster.
The bell is better known by the nickname
Big Ben, which is almost universally mistakenly
applied to the Clock Tower.
The name Big Ben was given to a 14.5 tonne
(16 ton) hour bell, cast on 10 April 1856
in Stockton-on-Tees by Warner's of Cripplegate.
The bell was never officially named, but
the legend on it records that the commissioner
of works, Sir Benjamin Hall, was responsible
for the order. Another theory for the origin
of the name is that the bell may have been
named after a contemporary heavyweight boxer
Benjamin Caunt. It is thought that the bell
was originally to be called "Victoria"
or "Royal Victoria" in honour
of Queen Victoria, but that an MP suggested
the nickname during a Parliamentary debate;
the comment is not recorded in Hansard.
Since the tower was not yet finished, the
bell was mounted in New Palace Yard but
the bell cracked under the striking hammer,
and its metal was recast at the Whitechapel
Bell Foundry as the 13.76 tonne (13.54 ton
(long), 15.17 ton (short)) bell, which stands
at a height of 2.2 metres with a diameter
of 2.9 metres, and it is still in use today.
The new bell, which chimes on A, was mounted
in the tower alongside four quarter-hour
bells, the ring of bells that ring the familiar
Along with the main bell, the belfry houses
four quarter bells which play the Westminster
Quarters on the quarter hours. The four
quarter bells are G sharp, F sharp, E, and
B (see note). They play a 20-chime sequence,
1-4 at quarter past, 5-12 at half past,
13-20 and 1-4 at quarter to, and 5-20 on
the hour. Because the low bell (B) is struck
twice in quick succession, there is not
enough time to pull a hammer back, and it
is supplied with two wrench hammers on opposite
sides of the bell.
Similar turret clocks
A 6 metre (20 ft) metal replica of the
clock tower, known as Little Ben and complete
with working clock, stands on a traffic
island close to Victoria Station. Several
turret clocks around the world are inspired
by the look of the Great Clock, including
the clock tower of the Gare de Lyon in Paris
and the Peace Tower of the Canadian Parliament
Buildings in Ottawa.
A clock tower similar to Big Ben is the
Joseph Chamberlain Memorial Clock Tower
of the University of Birmingham, England.
Often referred to as "Old Tom"
or "Old Joe", it is around three
quarters of the size of Big Ben. Its four
faces are each seventeen feet in diameter.
Baby Big Ben is the Welsh version of Big
Ben at the pierhead in Cardiff. Its mechanism
is almost identical to the one which powers
the Big Ben clock in London.
There are other replicas, one of the finest
is a two-third exact replica of the movement
made by Dent located in the Queens Royal
College Trinidad. There is another in Zimbabwe.
The 47 metre tower of the City Hall in
Pietermaritzburg, South Africa, contains
a quarter chime Westminster tower clock
and carillon manufactured by Gillett and
Johnston of Croydon. Its four faces are
each three metres in diameter.
The clock is famous for its reliability.
This is due to the skill of its designer,
the lawyer and amateur horologist Edmund
Beckett Denison, later Lord Grimthorpe.
As the clock mechanism, created to Denison's
specification by clockmaker Edward John
Dent, was completed before the tower itself
was finished, Denison had time to experiment.
Instead of using the deadbeat escapement
and remontoire as originally designed, Denison
invented the double three-legged gravity
escapement. This escapement provides the
best separation between pendulum and clock
mechanism. Together with an enclosed, wind-proof
box sunk beneath the clockroom, the Great
Clock's pendulum is well isolated from external
factors like snow, ice and pigeons on the
clock hands, and keeps remarkably accurate
The idiom of putting a penny on, with the
meaning of slowing down, sprang from the
method of fine-tuning the clock's pendulum.
The pendulum carries a small stack of old
penny coins. Adding or subtracting coins
has the effect of minutely altering the
position of the bob's centre of mass, the
effective length of the pendulum rod and
hence the rate at which the pendulum swings.
Adding or removing a penny will change the
clock's speed by 2/5th of one second per
Despite heavy bombing the clock ran accurately
throughout the Blitz. It slowed down on
New Year's Eve 1962 due to heavy snow, causing
it to chime in the new year 10 minutes late.
The clock had its first and only major
breakdown in 1976. The chiming mechanism
broke due to metal fatigue on 5 August 1976,
and was reactivated again on 9 May 1977.
During this time BBC Radio 4 had to make
do with the pips.
It stopped on 30 April 1997, the day before
the general election, and again three weeks
On Friday, 27 May 2005, the clock stopped
ticking at 10.07 pm, possibly due to hot
weather (temperatures in London had reached
an unseasonal 31.8 °C (90 °F). It
resumed keeping time, but stalled again
at 10.20 pm and remained still for about
90 minutes before starting up again.
On 29 October 2005, the mechanism was stopped
for approximately 33 hours so that the clock
and its chimes could be worked on. It was
the lengthiest maintenance shutdown in 22
There were other short stoppages but the
practice of the publicity department of
the Houses of Parliament to attribute problems
to weather and other reasons outside of
their control makes it difficult to be sure
why. Ex employees of Thwaites & Reed
who looked after the clock for 30 years
say problems were caused by a major overhaul
for the millennium being shelved and never
done. Thwaites & Reed say they have
the exact details of what was needed, but
they seem reluctant to make public their
records even though their older records
are on loan to the Guildhall Library in
London for everyone to see.
Big Ben's "Quarter Bells" were
taken out of commission for four weeks starting
at 0700 hrs GMT on 5 June 2006, as a bearing
holding one of the quarter bells was damaged
from years of wear and needed to be removed
for repairs. During this period, BBC Radio
4 broadcast recordings of British bird song
followed by the pips in place of the usual
On August 11, 2007, Big Ben went silent
and temporarily also stopped keeping time
for maintenance that lasted 1 month. The
bearings that help sound the chime on each
hour were replaced, for the first time since
installation. During the maintenance
works, the clock was not driven by the original
mechanism, but by an electric motor. Once
again, BBC Radio 4 had to make do with the
pips during this time.
The Clock Tower is a focus of New Year
celebrations in the United Kingdom, with
radio and TV stations tuning to its chimes
to welcome the start of the year. Similarly,
on Remembrance Day, the chimes of Big Ben
are broadcast to mark the 11th hour of the
11th day of the 11th month and the start
of two minutes' silence.
For years ITN's "News at Ten"
began with an opening sequence which featured
the Clock Tower and Big Ben with the chimes
punctuating the announcement of the news
headlines. The Big Ben chimes are still
used today during the headlines and all
ITV News bulletins use a graphic based on
the Westminster clock face. Big Ben can
also be heard striking the hour before some
news bulletins on BBC Radio 4 (6pm and midnight,
plus 10pm on Sundays) and the BBC World
Service, a practice that began on 31 December
1923. The chimes are sent in real time from
a microphone permanently installed in the
tower and connected by line to Broadcasting
Big Ben can be used in the classroom to
demonstrate the difference between the speed
of light and the speed of sound. Someone
visiting London who stands at the bottom
of the clock tower will hear the chimes
of Big Ben approximately one-sixth of a
second later than the bell being struck
(assuming a bell height of 55 metres). However,
using a microphone placed near the bell
and transmitting the sound to a far away
destination by radio (for instance New York
City or Hong Kong), that location will hear
the bell before the person on the ground.
In fact, if the recipient were to echo the
sound back to the observer on the ground,
the bell would be heard on the radio before
the natural sound reached the observer.
(Example: New York City is 5,562 kilometres
(3,456 mi) from London, and radio waves
will reach New York in 0.018552 seconds;
round trip is 0.037105 seconds, compared
with 0.1616 seconds for the natural sound
to reach the ground.)
Londoners who live an appropriate distance
from the Clock Tower and Big Ben can, by
means of listening to the chimes both live
and on the radio or television, hear the
bell strike thirteen times on New Year's
Eve. This is possible due to what amounts
to a one strike offset between live and
electronically-transmitted chimes by virtue
of a combination of digital coding and decoding
and satellite transit delay. Guests are
invited to count the chimes aloud as the
radio is gradually turned down.
An image of the clock tower was also used
as the logo for London Films.
In Japan, Big Ben's chime is used as the
chime for school bells from kindergarten
In 2005, a terrorist manual was found in
the home of Abu Hamza al-Masri, marking
Big Ben, the Statue of Liberty and the Eiffel
Tower as terrorist targets. In his trial
at The Old Bailey in 2006 he denied all
knowledge of their being targets.