Big Ben in London is a famous landmark because at one time the clock was the biggest in the world. As of 2014, Big Ben is still considered the largest clock in the United Kingdom. Although many people refer to the Clock Tower as Big Ben, this name actually applies to the Clock Tower's hour bell.
There were two hour bells made in the 1850s because the original one cracked. It is believed that the hour bell was nicknamed Big Ben after either Commissioner of Works Sir Benjamin Hall,or boxer Benjamin Caunt, but there is no documented evidence that supports this. There also are four other bells associated with this clock, but they are quarter bells.
In the mid-19th century, the clock was installed and it was simply called the Clock Tower. The tower has a height of 316 feet and the diameter of the clock faces is nearly 25 feet. In 2012, its name was changed to the Elizabeth Tower in honor of Queen Elizabeth II's Diamond Jubilee.