Clock towers are a common sight in many parts of the world with some being iconic buildings like the one in London commonly called 'Big Ben' (although it is correctly called the Elizabeth Tower as Big Ben is the bell inside the tower). Clock towers are a specific type of building which houses a turret clock and has one or more clock faces on the upper exterior walls. Many clock towers are freestanding structures but they can also be adjoining or on top of another building. The tallest clock tower in the world is the recently constructed Makkah Clock Royal Tower, standing 601 m or 1,971 feet high.
It is important to distinguish between clock towers and other buildings which may have clocks or clock faces attached to them. Many buildings have had clocks added to an existing structure. Although the resulting structure is often seen to be a clock 'tower' they are not the same sort of structure. Therefore: A clock tower is a tower specifically built with one or more (often four) clock faces. Clock towers can be either freestanding or part of a church or municipal building such as a town hall. The mechanism inside the tower is known as a turret clock. It often marks the hour (and sometimes segments of an hour) by sounding large bells or chimes, sometimes playing simple musical phrases or tunes.