The "Stelling van Amsterdam" is a military defense line around the city of Amsterdam, and is based on temporary flooding the land with water together with armed forts to control the access roads. Built between 1883 and 1920, it consists of dikes, canals, locks, as well as 45 forts over a length of 135 km (84 miles). With the development of newer technology, in particular the airplane, the defense line became obsolete and was released from its military status. Today the forts are used as restaurants, art galleries, museums, and for other purposes.