The Petronas Towers in Kuala Lumpur rose on the former Selangor Turf Club racetrack and were the tallest buildings in the world from 1998 to 2004, and they remain the tallest twin towers. The Malaysian government asked architect Cesar Pelli for an icon that reflected Malaysia’s Muslim culture, and he based the 88-story floor plan on the Rub el Hizb, an eight-pointed star of two overlapping squares, adding rounded scallops to make usable office space. Planning began on January 1, 1992, but test boreholes revealed that half the site sat on decayed limestone that dropped off like an underground cliff. The builders shifted both towers 61 meters onto the soft rock side and drove 104 concrete piles per tower, 60 to 114 meters deep, beneath a raft foundation poured continuously for 54 hours.

With a six-year deadline, Tower 1 went to a Japanese consortium led by Hazama and Tower 2 to a South Korean consortium led by Samsung C&T, which reached the top first despite a one-month handicap. Steel was too expensive, so the towers use Fazlur Rahman Khan’s tube-in-tube system in high-strength concrete. When one batch failed a strength test, work stopped at a cost of $700,000 a day and a finished floor was demolished. On September 12, 2001, a bomb threat forced both towers to evacuate at once, exposing the limits of the stairwells. Later the towers drew Felix Baumgartner’s 1999 BASE jump and Alain Robert’s climbs.

• Why a 54-hour pour could not pause without creating a fatal cold joint in the foundation
• Three on-site concrete plants set up so a bad batch could never stop construction again
• The 750-ton double-decker skybridge at levels 41 and 42, lifted over three days in July 1995 and built to slide as the towers sway
• Double-decker elevators serving odd and even floors, and the post-2001 plan to use elevators in evacuations
• Alain Robert arrested on the 60th floor in 1997 and 2007 before reaching the top of Tower 2 in 2009