In December 1952, bus driver Albert Gunter was on the south leaf of London’s Tower Bridge when it began to rise, and he floored the number 78 double-decker across a three foot gap, dropping six feet onto the north leaf. The bridge was born from a crisis: by the late 1800s nearly 40 percent of London lived east of London Bridge, but a fixed crossing would block tall ships from the Pool of London. A parliamentary committee formed in 1876 rejected more than 50 designs, including one from Joseph Bazalgette, before approving the plan of architect Horace Jones and engineer John Wolfe Barry in 1884, a hybrid of suspension spans, cantilevered high walkways, and a central bascule.

Construction took eight years from 1886, with about 432 workers a day, and ten men died. The Gothic stone is cladding over 11,000 tons of steel, required by Parliament to match the Tower of London. Its high walkways drew pickpockets and gamblers and closed in 1910, bombs knocked out the hydraulics in 1940, and pilots flew through the gap in 1912, 1968, and 1973. In 1997 the bridge opened for the sailing barge Gladys and split President Bill Clinton’s motorcade in half, because an 1885 act gives river traffic absolute priority.

• How steam engines pumped water to 750 psi into hydraulic accumulators that stored energy to lift each 1,000 ton bascule
• The RAF pilot who flew a Hawker Hunter jet through the bridge in 1968 to protest a missing flypast
• Albert Gunter’s reward for saving his passengers: a bonus of 10 pounds
• The 1974 switch to electro-hydraulics and the piezoelectric sensors that weigh trucks as they cross
• The myth that Robert McCulloch thought he had bought Tower Bridge, and a lamp post that is really a chimney for a hidden guard room