Clash of the Super Tower Arcologies

Above is pictured the Ultima Tower, a 500 story, 10,560 foot tower meant to house a million residents. Cost in 1991 dollars: $150 billion. Source

At 13,123 feet high, the massive, mountain-shaped building envisioned by Japan's Taisei Construction Company would overshadow Mount Fuji itself by nearly 700 feet. That's the equivalent of NINE Empire State Buildings stood one upon the other!

The building, known as the X-Seed 4000, is designed to house up to one million residents on as many as 800 floors! Designers have had to consider tricky questions of temperature and pressure differentials between the base and topmost floors, and are looking to utilize solar power to solve these and other critical issues. The cost, you ask? Somewhere between $300 and $900 billion...Source

Either structure is meant to house a million inhabitants, but the X-Seed is a bit taller and perhaps more carefully engineered up to this point.A more modest arcology is the Crystal Island project designed for Moscow by Foster and Partners.

Paolo Soleri envisioned arcologies as solutions to the problem of urban sprawl, and destruction of natural habitat by human development. He designed arcologies for land, sea, and outer space. But until significant advances are made in strength vs. weight vs. cost of building materials, truly huge arcologies will likely have to wait.