Napoleon I, you will remember, took Pope Pius VI prisoner in an attempt to finish off the Church, or at least control it. The poor man died in captivity in Valence, August 29, 1799. Rome at that time was being fought over between the Neapolitans and French, so it was inconceivable to hold a new election there. The Austrians had got hold of Venice in 1797, and many of the cardinals had taken refuge there, including the now penniless Cardinal Henry (King Henry IX) Stuart, Duke of York.
Rather generously, the Hanovers eventually provided a pension for him (kindness or bad conscience?).
Anyway, Venice seemed the obvious place to hold the new conclave, under the circumstances.
The Holy Roman Emperor (in the last throes of that ancient institution) was happy enough to agree to the conclave taking place in what was now his territory, and actually coughed up 24,000 scudi for the expenses. Naturally he assumed that this would give his candidate a certain chance of success; important, because Austria had nabbed some of the Papal States for herself and wanted to hang onto them.
Thirty five or so of the 46 extant cardinals entered the conclave. It didn't go well. Herzen, the Viennese Cardinal, and Albani, another pro-Austrian Cardinal, tried hard to get the other Cardinals to elect Mattei of Ravenna, who was known to be pro-Austrian. This scandalized the electors, and, exceptionally, the conclave was suspended for 11 or 12 days while a messenger was sent to Vienna to consult with the Emperor. It was not unknown (indeed it was a recognized right of a Catholic sovereign) to exercise a veto in a conclave. It last happened in 1903. But actually to break a conclave to consult a sovereign in mid-course was unheard of. There was deadlock.
Finally Cardinal Chiaramonti of Imola was elected as a compromise candidate, and took the name Pius VII. He was known to have been sympathetic to the French Revolution; he had had printed on his writing paper 'liberty' and 'fraternity', and under the Cisalpine Republic had described himself as Citizen-Cardinal. Despite differences, heated arguments, and an imprisonment, once Pope, he actually got on personally rather well with Napoleon.
The conclave had begun on 30 November 1799, and finally the new Pope was elected on 14 March 1800.
The Emperor, furious that his candidate had not been elected, refused permission for the coronation to take place in St Mark's Basilica, so it happened here in Palladio's church of San Giorgio, with the overflow congregation assisting in gondolas from the Giudecca canal. There was, of course, no tiara, since Napoleon had confiscated all the treasures from Rome, and so, I seem to remember, they manufactured one out of papier maché.
The interior of San Giorgio, where the Coronation Mass took place. These days it seems pretty much abandoned to the tourists. There is a notice saying that Mass and all the offices take place in another chapel, and not in the lovely choir stalls behind the high altar.
A tiara given by Napoleon to Pius VII. I quote in full from this site, whence I got the pic.
"A gift from Napoleon Bonaparte to Pope Pius VII in 1805, the irony is that the tiara was made of treasure looted from the Vatican eight years before when French troops invaded the Papal States. Ostensibly, the gift was a gesture of atonement from Napoleon for the plunder nearly a decade earlier, but the base was so small Pius VII could not wear it--an intentional slight by Napoleon. Most of the original jewels adorning the tiara were replaced with cut glass during the 19th century, but the huge milled emerald supporting the diamond-studded cross at the top--the Emerald of Gregory XIII--remains (and had actually been mounted on several different tiaras used by Pius VII's predecessors). Also stripped from the tiara were three engraved bas-reliefs that depicted scenes of Napoleon's coronation as Emperor of France, re-legalization of public worship in France and the signing of a treaty between the Vatican and France. I think it's safe to say that even without the original jewels and engravings, this is still an overwhelmingly opulent piece. Even if nobody ever got to wear it."