X-Seed 4000 is a visionary megatall skyscraper.^[1]

Its proposed 4 km height, 6 km wide sea-base, and 800 floors capacity that could fit 500,000 to 1,000,000 people. This structure would have been made using 3 billion kilograms of steel.

It was designed for Tokyo, Japan. The design was made by the Taisei Corporation in 1995. It was designed as a future-like environment combining ultra-modern and technological living and interaction with wildlife and nature.^[2] Methods of transportation within the X-seed would most likely include MagLev trains.

"The X-Seed 4000 'is never meant to be built'." says Georges Binder, managing director of Buildings & Data, a firm which compiles data banks on buildings worldwide. "The purpose of the plan was to earn some identification for the firm, and it worked."^[3]

Unlike other skyscrapers, the X-Seed 4000 would be forced to protect its occupants from large internal/external air pressure effects and weather rising that its great elevation would cause. Its design calls for the use of solar power to keep internal environmental conditions.^[4]

As the proposed site for the structure is located in the Pacific Ring of Fire, the most active volcano range in the world, the X-Seed 4000 would be weak to earthquakes and tsunamis.

A sea-based location and a Mount Fuji shape is some of this building's other major design features. The real Mount Fuji is land-based and is 3,776 metres in height. This is 224 metres shorter than the X-Seed 4000.

X-Seed 4000 is planned to be twice the height of the Shimizu Mega-City Pyramid at 2,004 metres.

The Shimizu Mega-City Pyramid for Tokyo was proposed in 2007. This plan also faces most of the same problems as X-Seed 4000.

Others that may be in the top 5 man-made structures are:

• Ultima Tower, 3,218 metres in San Francisco
• Dubai City Tower, is 2,400 metres
• Bionic Tower, is 1,228 metres in either Hong Kong or Shanghai