Big Ben is not the tower but the great bell inside it. After fire destroyed the old Palace of Westminster in October 1834, architect Charles Barry won the rebuild and turned to Augustus Pugin, who designed the Gothic clock tower before his mental collapse and death. Completed in 1859, the 316 foot tower of brick and Anston limestone leans about 20 inches to the northwest on London clay, a tilt worsened by Jubilee Line tunneling in the 1990s. Edmund Beckett Denison and Astronomer Royal George Airy designed a clock with 14 foot copper minute hands, and Denison’s unpatented double three-legged gravity escapement kept wind on the hands from disturbing the pendulum.

The first 16 ton bell, cast by John Warner and Sons in 1856, cracked during testing. The 13.5 ton replacement from the Whitechapel Bell Foundry was hauled up the tower over 18 hours and first rang in July 1859, then cracked two months later after Denison used a hammer of about 440 pounds, more than twice the foundry’s limit. Workers rotated it an eighth of a turn and fitted a lighter hammer, and the unrepaired crack still shapes its tone. The clock kept running through a 1941 bomb strike, though starlings slowed it in 1949, and a 2017 to 2021 restoration grew from 29 million to nearly 80 million pounds.

• A stack of pre-decimal pennies on the pendulum, each shifting the clock by 0.4 seconds a day
• The Ayrton Light that told Queen Victoria when the Commons sat late, and a prison room where atheist MP Charles Bradlaugh was held in 1880
• Competing origins for the nickname: Sir Benjamin Hall or the boxer Ben Caunt
• Restorers finding asbestos, lead paint, and hidden war damage, and returning the dials from soot black to Prussian blue
• BBC broadcasts since 1923, 96 chimes for Queen Elizabeth II, and how radio and live sound can make noon strike 13