The X-Seed 4000 is a visionary skyscraper for what would be, if it was built, the tallest building in the world. The idea was initially created and developed by Peter Neville. Its proposed 4-kilometre (2.5 mi) height, 6-kilometre-wide (3.7 mi) sea-base, and 800-floor capacity could accommodate 500,000 to 1,000,000 inhabitants. This structure would be composed of over 3,000,000 tons of pure steel.It was designed for Tokyo, Japan by the Taisei Corporation in 1995 as a futuristic environment combining ultra-modern living and interaction with nature. Methods of transportation within the X-seed would most likely include MagLev trains.