The legislation in force provides for the protection of natural areas, not only for their scenic qualities but also as agricultural or environmental reserves. However, this strategic conservation of the rural landscape is not matched by similar conservation measures for the built fabric in large cities. This paper considers how to bring about, in a city with a major architectural heritage such as Barcelona, a programmatic change in a manner similar to what is happening in the rural environment, understanding and promoting the conservation of large urban areas as a form of strategic environmental conservation, as the reserving of area for the future and as part of an ecosystem.