Five of Canada's ten largest cities enforce height restriction laws. In Ottawa, skyscrapers could not be built above the height of the Peace Tower until the late 1970s, when the restriction was changed so that no building could overwhelm the skyline. In Montreal, skyscrapers cannot be built above the elevation of Mount Royal. The City of Vancouver has enacted view corridors which limit the height of buildings in most areas of downtown. The City of Edmonton had an elevation restriction, approximately above downtown, due to the proximity of the city centre airport, until it closed in November 2013.