Why is Big Ben so called ?

Although the name "Big Ben" is commonly used to refer to the famous clock at the top of St. Stephen´s Tower of the Houses fo Parliament in London, the nickname is more correctly applied to the bell within the tower.  It was named after Sir Benjamin Hall, who was the Chief Commissioner of Works at the time.

The orginal bell, cast in 1856 and weighing some 15 tons, was being tested in Palace Yard when it developed serious cracks and had to be scrapped.  The new bell, weighing a mere 13 tons, was installed in 1858.  There are also four Quarter bells in the clock tower weighing between 4 tons and 1 ton.