Clock towers are a specific type of structure that house a turret clock and have one or more clock faces on the upper exterior walls. Many clock towers are freestanding structures but they can also adjoin or be located on top of another building. Some other buildings also have clock faces on their exterior but these structures serve other main functions.
A clock tower in Erbil
Sarajevo Clock Tower
A clock tower in the Helsinki Central Station
The Tower of the Winds in Athens, built c. 50 BC during Roman Greece
A turret clock or tower clock is a clock designed to be mounted high in the wall of a building, usually in a clock tower, in public buildings such as churches, university buildings, and town halls. As a public amenity to enable the community to tell the time, it has a large face visible from far away, and often a striking mechanism which rings bells upon the hours.
Probably the most famous turret clock is located in the Elizabeth Tower at the north end of the Palace of Westminster in London and rings the bell "Big Ben"