London Bridge is the name of a series of bridges in London that have been built in roughly the exact same spot. The original London Bridge was built by the Romans, with the original city of Londonium growing outwards roughly from there.
After the Roman withdrawal, the bridge was re-built and collapsed numerous times before, in the 13th century, they decided to build a really epic new bridge to replace it. This bridge, like a number of other mediaeval bridges, was a “living bridge”: it was lined either side with multistorey buildings containing shops, businesses, and people’s homes! The actual road in the middle of the bridge was narrow, congested and dark (in those days each successively higher storey of a building would slightly overhang the one below it, so the distance between buildings got narrower the further up you went). In order to try to control congestion, the authorities who controlled the bridge charged a toll to those who’d want to cross it. Not only this but also the sheer congestion of the bridge and surrounding streets meant that it was more common to use another means to cross the bridge anyway – paying a “wherry” in a little boat to row you across (and also to other parts of the Thames entirely, saving you the time you’d otherwise have had to spend navigating London’s streets). The bridge was also used to display the severed, tarred and boiled heads of traitors.
Over time, there came to be gaps in the bridge where buildings had come down, or burnt down, or been demolished or whatever with nothing built to replace them. This proved to be beneficial during the Great Fire of London, when the firebreak prevented the flames from spreading to Southwark. The nursery rhyme “London Bridge is Falling Down” seems to date back to around this time.
From 1670, efforts were made to improve traffic flow by mandating that northbound and southbound traffic stick to different halves of the road. In 1680, nearly all the buildings were rebuilt to sit further back from the roadway (creating more road space) and to teeter over the river instead. The last new buildings on the bridge were built in 1745, but in 1756 the government authorised the City Corporation to buy out all the buildings in order to demolish them, and create an even wider roadway. This work was completed by 1761. But then they decided to build this huge-ass Great Arch that was so heavy that it weakened the integrity of the whole bridge and constant expensive repairs were required thereafter.
It was finally decided to replace the old medieval bridge, and in 1831 New London Bridge – a stone arch bridge designed by John Rennie – was opened, having been built 30m to the west of the original bridge. New access roads had to be built which turned out to be 3x as expensive as actually building the new bridge. Like the old bridge it was always extremely congested with traffic, and it also had problems with subsidence, the east side sinking faster than the west side for example.
When London City Council decided in the 1960s to replace New London Bridge, they also had the idea to sell the old one, in order to offset the coast of the new. New London Bridge was bought by some multimillionaire American, and the bridge was disassembled, shipped in pieces to Long Beach, trucked from there to Arizona, and reassembled (with a more modern steel frame on the inside) in Lake Havasu City.
The present-day London Bridge opened to traffic in 1973 and it is a completely unremarkable, unattractive bridge designed primarily for vehicular traffic.