The Palace of Westminster, the Clock Tower and Westminster BridgeThe 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.

The new Parliament was built in a Neo-gothic Italian 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 Hall. 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 Revival style, and is 315.9 ft high.

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 49 ft square raft, made of 9.8 ft thick concrete, at a depth of 13 ft below ground level. The four clock faces are 180 ft above ground. The interior volume of the tower is 164,200 cubic feet.

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 8.66 inches 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.

Faces
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. However, 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 face of the Great Clock of Westminster. The hour hand 9 ft long and the minute hand is 14 ft long. The clock and dials were designed by Augustus Pugin. The clock faces are set in an iron frame 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 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.

Big Ben is actually the name of the huge bell in the clock of the St. Stephen's Tower. When Parliament is sitting at night, a light shines above the clock for all to see.