London

Marble Arch
Before John Nash, the brains behind Regent Street, intended this structure to be… well, a Regent’s treat. His arch started life in 1833 as a ceremonial gateway to Buckingham Palace.
After A decade later, the grand portal was reconstructed north-east of Hyde Park. It remains there to this day, alone and unloved on a busy traffic island.

Wellington Arch
Before The beefier cousin of Marble Arch stands marooned on the island at Hyde Park Corner. And has done since 1829, though not quite in the same place.
After The Victorians were quite prepared to move their buildings a few feet to the right if the fancy took them, and 1883 saw the great arch tiptoeing a few steps east and swinging round by 90 degrees.
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London Bridge
Before It may not have fallen down, but the famous span has been dismantled, rebuilt and moved around several times. The original Old London Bridge is long gone, but a chunk can still be found in Victoria Park, Hackney.
After The replacement (built in 1831 by John Rennie, 100 yards upstream of the original) got shipped to America in the ’70s. Rumours that they thought they were buying Tower Bridge are denied by Yanks, but keenly championed by cabbies and the bloke down the pub. It is now in Lake Havasu City where it is Arizona’s second biggest tourist attraction.

Temple Bar
Before This Christopher Wren job started out in 1672 over in Fleet Street, where it marked the boundary between the City and Westminster, and was often embellished with the heads of traitors.
After By 1878, it had become a traffic nuisance so was taken down and shifted to Theobalds Park, Hertfordshire. The rural retreat began to pall and the gateway returned home two years ago. It now stands in the City’s Paternoster Square.

Crosby Hall
Before Thomas More bought it, Richard III hatched plots in it and the Edwardians wanted to demolish it as it was getting in the way of a new bank. So some bright spark decided to move this fifteenth-century banqueting hall from Bishopsgate to a new site in 1910.
After To Cheyne Walk, Chelsea, in fact, where it is now a private residence on land previously owned by Thomas More.