London Bridge in 1616. Drawing by Claes Van Visscher.
Yesterday’s terror attack on London Bridge follows by about two and a half months a similar attack on Westminster Bridge, four bridges east of London Bridge. Thirty-three bridges span the River Thames in Greater London. The most famous is Tower Bridge, near the Tower of London. The bridge that was taken down and rebuilt in Arizona is not, as some think, the Tower Bridge but an earlier version of the London Bridge attacked last night. That London Bridge was auctioned off to the founder of a planned community in Arizona. The first London Bridge was built in A.D. 50 and (Wikipedia says) rebuilt in 1209 and 1831. The just-victimized London Bridge replaced the 1831 bridge in 1973, after it was found to be sinking into the riverbed of the Thames.
In fact, the old ditty “London Bridge Is Falling Down” does relate to the instability of the bridge that was rebuilt in Arizona. It had been considered “at risk” for centuries. The song has been traced back to the 17th century. In those days, London Bridge had buildings lining the span. Many states, such as Rhode Island, hyperventilate with regularity that their bridges are at risk of falling down. All bridges are at risk of falling down, especially since bridge engineers use computers these days to calculate the strength requirement of bridges before they are built. (Today’s engineers may be more likely to think that they can figure out those requirements exactly, whereas old bridges were engineered with a superabundance of strength because professional humility made for a commendable degree of caution.) I officially raise my eyebrows at Wikipedia’s assertion that the first London Bridge lasted from A.D. 50 to A.D. 1209, or that the 1209 version stood until 1831. Maybe they did.
On a bridgeworthy note, in 2016 a New York City-based artist, Leo Villareal, who designed the lighting for the San Francisco Bay Bridge, was chosen to light up the 17 bridges of central London. His plan appears encouragingly subdued, seeming to avoid the gaudy effects one might reasonably fear in a huge project of “the arts.” A video of it is on the Thames Leisure website.
The primary bridges of central London. (workflow.arts.ac.uk)
Photo of the Thames showing major spans. Tower Bridge is the bottom. (Wikipedia)
Architecture Here and There 
I’m sure you are right, Peter. The two London Bridges upon which I cast potential aspersions as to their survivability probably did not deserve such skepticism.
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I have walked across the Ponte Fabriccio in Rome, from the Tiber Island to the Campus Martius , built 2,079 years ago and named after the Roman Superintendent of Roads and Bridges in charge at the time. http://www.sovraintendenzaroma.it/i_luoghi/roma_antica/monumenti/ponte_fabricio
I don’t doubt the Romans ability to build a bridge which survived only 1,159 years.
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