An observation tower is a structure used to view events from a long distance and to create a full 360 degree range of vision. They are usually at least 20 metres (65.6 ft) tall and made from stone, iron, and wood. Many modern towers are also used as TV towers, restaurants, or churches. The towers first appeared in Germany at the end of the 18th century, and their numbers steadily increased, especially after the invention of the elevator. Observation towers that are used as guard posts or observation posts over an extended period to overlook an area are commonly called watchtowers instead.