Towers are tall human-made structures that are always taller than they are wide, usually by a significant margin. Towers are generally built to take advantage of their height, and can stand alone or as part of a larger structure.

Towers have been used by mankind since prehistoric times. The oldest known may be the circular stone tower in walls of Neolithic Jericho (8000 BC). Some of the earliest surviving examples are the broch structures in northern Scotland, which are conical towerhouses. These and later examples from Phoenician and Roman cultures emphasised the use of a tower in fortification and sentinel roles. For example, watchtower elements are found at Mogador from the first millennium BC, derived from Phoenician or Carthaginian origins. The Romans utilised octagonal towers as elements of Diocletian's Palace in Croatia, which monument dates to approximately 300 AD, while the Servian Walls (4th century BC) and the Aurelian Walls (3rd century AD) featured square ones. The Chinese used towers as integrated elements of the Great Wall of China in 210 BC during the Qin Dynasty.

A noted incomplete tower is the Hassan Tower in Morocco, where work was abandoned in 1199 AD, and the tower stands today as a monument in its incomplete state. Another well known tower is the Leaning Tower of Pisa in Pisa, Italy built from 1173 until 1372. The Himalayan Towers are stone towers located chiefly in Tibet built approximately 14th to 15th century.

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