When the London Mayor’s office invited Anish Kapoor and Cecil Balmond to submit an entry, it said the Mayor was “looking for an icon to match the Eiffel Tower”. That was an irresistible challenge for the pair, who had collaborated before. They were partly inspired by the Tower of Babel – a seemingly impossible structure reaching up beyond the clouds. “We tried to rethink the tower so that the whole structure is in a twist, always off kilter, never quite vertical,” says Kapoor. “That takes a certain amount of engineering prowess to put together,” Balmond adds.