The world’s tallest skyscraper would be five times bigger than the unparalleled Burj Khalifa in Dubai if the ‘dream’ proposal created in 1995 ever becomes a reality
Liam McInerney Content Editor
04:00, 03 Jan 2026Updated 07:42, 03 Jan 2026
A concept design for the X-Seed 4000(Image: Reuben Petty /LINKEDIN)
The world’s tallest current building is the Burj Khalifa in Dubai – but a concept created three decades ago would be five times the height of that if it ever gets built.
The design, which first came to light in 1995, is called the X-Seed 4000, and it would be by far the tallest skyscraper ever made. That’s because it would rise a mind blowing 4km (or 13,123ft/2.5 miles) into the sky making it just under half the height of Mount Everest.
The Japanese construction firm behind it, Taisei Corporation, reportedly wanted it to float on Tokyo Bay, and other locations in Asia were considered.
Their hugely ambitious project even proposed to provide homes for between 500,000 and one million people who would live in the 800 floors.
Some 3,000,000 tons of steel would have been required for the complex task and internal air pressure regulations would have been considered for residents to avoid altitude illnesses.
It would dwarf the Burj Khalifa which stands at 828 metres (2,717ft) (Image: Newsburst/Wikipedia)
The floating metropolis, stretching 6km wide, was recently discussed on LinkedIn where Reuben Petty provided insight into the dream that never became a reality.
He said: “Its form was inspired by Mount Fuji, featuring a broad, stable base gradually tapering to a majestic peak. This pyramidal shape was not purely aesthetic; it was intended to provide structural stability against the forces of the ocean and potential seismic activity, a significant concern in the Tokyo Bay area.”
The brains behind it hoped it would be a self-contained artificial island supported by floating caissons.
And rather than just be made up of apartments, the vision was for it to act like a city all of its own, with business centres, commercial districts, recreational facilities and research institutions all being on site.
Rumours circulated in 2007 that Taisei intended to follow up with the grand plan, but these were soon put to bed.
Concepts for the ambitious project (Image: BRIGHT SIDE Series/Youtube)
George Blinder, managing director of Buildings & Data, claimed at the time: “It was never meant to be built. The purpose of the plan was to earn some recognition for the firm, and it worked.”
And confirming that the skyscraper was not back on the radar, Shohei Ogawa, a planning manager at Taisei, said X-Seed 4000 was “on the shelf now”.
He added: “It was our dream proposal for the technological advances we thought that could happen in the future.”
One architect and author of a Skyscraper: Vertical Now, Erik Howeler, told Architectural Record that it was “possible” from an engineering perspective to build such a tall building.
However, feasibility wise, he believed the estimated $1 trillion cost would be difficult, along with getting permission to build such a massive structure. He added: “Tall buildings create a downdraft at their bases, and cast long shadows.”
The Burj Khalifa is the tallest man made structure in the world(Image: Getty Images)
The project, which also raised safety and environmental concerns, was discussed on a Reddit thread where one user wrote: “This literally looks like the city seen in high charity mission in Halo 2.”
Another said: “That’s genuinely just the star harvester from Transformers 2.”
A third person said: “Imagine the elevator not working and you live on the 657th floor.”
One comment added: “Ah yes, let’s waste resources to build some massive building.”