30 St Mary Axe (the Gherkin)

Foster and Partners won the commission in 1997 for a site that had stood empty since April 1992, when an IRA bomb devastated the Baltic Exchange building that previously occupied it. Rather than repeat the orthodox point-block tower plan, engineer Arup and the design team wrapped the 180-metre, 41-storey office in a diagonally braced steel diagrid, doing away with internal corner columns and letting the skin itself carry lateral load. The plan swells outward from a narrow base and tapers again toward the crown, a bulging profile driven less by whimsy than by wind engineering: the curve reduces downdraughts at street level and lets six triangular light wells spiral up through the floors, drawing daylight deep into the plan and ventilating the offices naturally for part of the year. London nicknamed it the Gherkin before it opened in April 2004, and the name stuck harder than the building's registered one, Swiss Re, the reinsurer that first occupied it. It became an instant fixture of the City skyline and one of the most photographed towers in Europe.