IN 1956, FRANK LLOYD WRIGHT conceived of the Mile-High Building. Since Wright, others have followed with concepts that approach one mile in height. Foster and Partners have proposed the Millennium Tower and Cervera & Pioz have proposed the Bionic Tower. Realistic steps toward this extreme height are incremental, with what was formerly the tallest building in the world, Taipei 101, designed by C.Y. Lee and Partners, at 508 m (1667 ft). At 828 m (2716 ft), the Burj Khalifa, designed by SOM and completed in 2010, has significantly surpassed this height.