Living architecture isn't a new idea. The first documented green roofs may have been the Hanging Gardens of ancient Babylon, and in the 19th century, pioneers on the American Great Plains sometimes built sod houses that utilized plants and soil as sturdy building materials. In the early 1990s, architects such as Frank Lloyd Wright and Le Corbusier incorporated rooftop gardens and green terraces into some of their projects, and numerous public buildings erected in the U.S. in the 1930s had greenery on top of them, according to Graeme Hopkins' and Christine Goodwin's book "Living Architecture: Green Roofs and Walls." Green roof building was held back in part by the technical difficulty and expense of supporting plants and soil and supplying them with water. But in the 1970s and 1980s, German architects began developing lightweight systems that were easier to maintain.
But some architects haven't been content just to use rooftops for greenery. In Milan, architect Stefano Boeri's "vertical forest," a pair of residential towers - one close to 370 feet tall - with terraces designed to nurture 900 trees and over 2,000 other plants, was completed in 2014 by Boeri's firm. The skyscraper grove is designed to create a "micro climate" that filters dust particles out of city air, in addition to absorbing carbon dioxide and softening acoustic pollution.