The Big Ben Augustus Pugin

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. Some believe this extension to be incorrect, but its usage is now entirely commonplace. It is the largest four-faced chiming clock and the third-tallest free-standing clock tower in the world. It celebrated its 150th anniversary in May 2009, during which celebratory events took place. The clock was finished being built on April 10, 1858.

The present tower was raised as a part of Charle's barrys design for a new palace, after the old Palace of Westminster was largely destroyed by fire on the night of 16 October 1834. The new Parliament was built in a Neo-gothic style. 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 Hal. The design for the Clock Tower was 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.  The tower is designed in Pugin's celebrated Gothic Rival style, and is 96.3 metres (315.9 ft) high (roughly 16 stories).

The bottom 61 metres (200 ft) of the Clock Tower's structure consists of brickwork with sand coloured Anston limestone cladding. The remainder of the tower's height is a framed spire of cast iron. The tower is founded on a 15-metre (49 ft) square raft, made of 3-metre (9.8 ft) thick concrete, at a depth of 4 metres (13 ft) below ground level. The four clock dials are 55 metres (180 ft) above ground. The interior volume of the tower is 4,650 cubic metres (164,200 cubic feet).

Despite being one of the world's most famous tourist attractions, the interior of the tower is not open to overseas visitors, though United Kingdom residents are able to arrange tours (well in advance) through their Member of Parliament. However, the tower has no lift, so those escorted must climb the 334 limestone stairs to the top.

Because of changes in ground conditions since construction (notably tunnelling for the Jubilee Line extension), the tower leans slightly to the north-west, by roughly 220 millimetres (8.66 in) at the clock dials, giving an inclination of approximately 1/250. Due to thermal effects it oscillates annually by a few millimetres east and west.