This year, the centrepiece of the mammoth urban engineering project that ensued -- the resplendent, five-kilometre (three-mile) "Ringstrasse" boulevard ringing old Vienna -- turns 150.
With its dizzying mix of palaces, museums and public buildings in a chocolate box of different styles, the "Ring" is the "most beautiful boulevard in the world", the tourist board says.
The Austrian capital is marking this with special exhibitions, showing how this street beloved of tourist and architecture aficionados -- including Hitler -- has played a central role in the city's happiest and darkest days.
'Like a museum'
Following Franz Joseph's decree, the city walls that had kept out two marauding Turkish armies -- but not Napoleon -- were torn down, opening up the claustrophobic centre.
Inspired by Baron Haussmann's renovation of Paris and by Ludwig I's transformation of his Bavarian capital Munich, Vienna summoned the finest architects of the day -- Gottfried Semper, Theophil Hansen and Heinrich von Ferstel.
The theme chosen was "historicism", giving the designers free rein to give it all they had with designs inspired by bygone epochs in architecture -- and with no expense spared either financially, or in scale.
The Ringstrasse was opened by the Kaiser on May 1st, 1865. Photo: ÖNB
So what sprang up was the soaring "Flemish-Gothic" city hall, a "neo-Renaissance" university, a "neo-Romantic" opera house and the "neo-Classical" parliament, a Hellenist's wet dream complete with ripped Greek heroes and an imposing Diana statue.
Others include the hallowed Burgtheater, the mighty Natural History Museum and its twin the Museum of Art History, the Neue Burg extension to the Hofburg palace and the Votivkirche church -- all in different styles, but still fitting together.
"It is fantastic, like a museum of architecture," said Rainald Franz, art and architecture historian at the Museum of Applied Arts (MAK). "The aim was to say to the world this is an international metropolis."
Indeed, the Ringstrasse became the main stage for Vienna's golden era, the boulevard's glittering cafes a haven for the intellectual elite of the day like composer Gustav Mahler, the father of psychoanalysis Sigmund Freud or artist Gustav Klimt.
And filling the gaps between the public buildings were plush palaces erected by a new, confident and ostentatious class of Viennese grown rich from the vast empire's rapid industrialisation, many of them Jews.
These included for example the Ephrussis, the banking family made famous by Edmund de Waal's bestselling 2010 family memoir "The Hare with Amber Eyes".
Their former home still stands today -- inhabited by Casinos Austria and next to a McDonald's.
But according to Gabriele Kohlbauer-Fritz, curator of an upcoming exhibition -- "Ringstrasse: A Jewish Boulevard" -- at Vienna's Jewish Museum, this splendour was a facade, and not just for the city's Jews.
"On the one hand there was this wonderful Ringstrasse but at the same time the masses had to fight to survive, both Jews and non-Jews," she told AFP.
Most of the bricks for the Ringstrasse's buildings were made in vast factories where workers, most of them Czech, would work in horrendous conditions for 15 hours a day, seven days a week, paid in company tokens, not money.
People living in "catastrophic" conditions, and the lower middle classes left behind by the Industrial Revolution, became "highly receptive" to anti-Semitism, sowing the seeds for the rise of the Nazis and the Holocaust, Kohlbauer-Fritz said.
The man behind that genocide first visited Vienna in around 1906 as a teenager, and was blown away by the Ringstrasse.
"For hours and hours I could stand in wonderment... The whole Ringstrasse had a magic effect upon me, as if it were a scene from the Thousand And One Nights," Hitler later recalled in "Mein Kampf".
He later lived in Vienna between 1908 and 1913, during which time he failed to get into the Academy of Fine Arts, stayed in a homeless shelter and sold respectable paintings of the many buildings on the Ring.
And when the failed artist returned in triumph on March 12, 1938 as Nazi dictator, he knew the best place to make a triumphant entrance and announce the "annexation" of his native country into the Reich -- the Ringstrasse and the balcony of the Neue Burg palace.
The same night, with the streets of Vienna ringing with shouts of "Heil Hitler"!, recounts de Waal in "The Hare with Amber Eyes", the first brownshirts barge into and ransack the Ephrussi Palace. It was a foretaste of the tragedy to come.
By Simon Sturdee, AFP
Click here for more information on Ringstrasse tours: http://www.wien.info/en/sightseeing/ringstrasse2015