Big Ben is the nickname for the great bell of the clock at the north-eastern end of the Palace of Westminster in London, and is often extended to refer to the clock or the clock tower as well. It is the largest four-faced chiming clock and the third-tallest free-standing clock tower in the world. 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 nickname Big Ben is the subject of some debate. The nickname was applied first to the Great Bell; it may have been named after Sir Benjamin Hall, who oversaw the installation of the Great Bell, or after boxing's English Heavyweight Champion Benjamin Caunt. Now Big Ben is used to refer to the clock, the tower and the bell collectively, although the nickname is not universally accepted as referring to the clock and tower.