By Bethany Bell
BBC News, Vienna
The grandeur of the imperial architecture of Vienna provides a perfect setting for establishing diplomatic relationships
Vienna's annual ball season is a time for diplomats and leading figures to gossip and become acquainted away from the political tensions of their normal routines. But this year, the upheaval in Egypt was high on the minds of many guests.
The magnificent, ceremonial apartments of Vienna's Hofburg Palace were full.
In the main ballroom, decorated with crystal chandeliers and frescos glorifying the long-dead Hapsburg emperors, women in silken gowns and men in black ties were crowded around the edge of the shining parquet dance floor.
The orchestra struck up that most Viennese of tunes, the Radetzky March. Seven United Nations security guards carrying the flag of the UN's nuclear agency, the IAEA, marched across the hall.
The annual International Atomic Energy Agency Staff Association Ball had begun.
Now some might find the idea of a ball for atomic scientists, nuclear inspectors and diplomats dedicated to uncovering, among other things, the facts about Iran's nuclear programme, a touch incongruous.
But this is Vienna, where even the city's rubbish collectors hold a ball.
And the international organisations that are based here, such as the IAEA and the Organisation for Security and Cooperation in Europe, do not want to be left out.
"Everyone knows how important ball season is in Vienna," one diplomat told me.
"Ours just adds a bit of international flair - and, of course, we are a charity ball. Anyone can buy a ticket."
This year's IAEA ball began with an apology by the Master of Ceremonies. An Egyptian band that was supposed to have performed at the opening had been unable to travel to Vienna because of the unrest in Egypt.
The IAEA's Yukiya Amano and his wife impressed onlookers
High on the minds of many guests was the absence of another Egyptian, Mohammed ElBaradei, the former director general of the IAEA and now one of the leaders of the opposition in Cairo.
For over a decade he served as patron of the IAEA ball, presiding over his staff as they danced the night away at the Hofburg palace.
"He always wore perfectly tailored suits," one of his former colleagues told me.
"He would do his duty and open the ball, a bit reluctantly because he is a shy man. And as far as I am aware, he never learnt to waltz."
The same cannot be said about the IAEA's new director general, the Japanese diplomat, Yukiya Amano.
During his time in Vienna, he has been taking dance classes. He and his wife, resplendent in a pale blue kimono, danced the first waltz before the floor was finally opened to the general public.
An in-house camera team followed the couple throughout the evening as they moved about the palace.
One of the ball guests looked on disapprovingly: "You know all this ceremony can go to your head a bit," he told me.
"Look at ElBaradei, who has gone off to try and be pharaoh in Egypt. It is so opportunistic."
But others disagreed.
"Mohammed is a man of conviction," one woman told me.
"He believes that winning the Nobel Peace Prize comes with a price.
"He didn't have to go back to Egypt. He could have stayed here in comfort. But he has a real sense of responsibility."
'Gossip and introductions'
I followed Mr Amano and his entourage into another ballroom, the Kleine Redoutensaal.
This white and gold baroque hall was the site of some of the lavish balls and parties given during the Congress of Vienna, which took place from 1814 to 1815.
Colonel Gaddafi's son (L) and Joerg Haider (R) at the Opera Ball in 2002
Monarchs and diplomats gathered here to redraw the map of Europe after the Napoleonic wars.
And during breaks in the protracted negotiations, they waltzed.
"The Congress dances," wrote one aristocrat, "but it does not progress."
Vienna's heyday as a capital of one of the great world powers is long gone. But the city nurtures its old traditions, partly for its tourists and foreign guests but in great part because the Viennese themselves enjoy them.
And the balls still serve as a place for gossip, and the exchange of introductions and information.
In early March, the Austrian chancellor and members of his government will attend the Opera Ball, the highlight of the Viennese social calendar.
A few years ago, I remember being intrigued to see Colonel Gaddafi's son, Saif al-Islam, attending with his host, the far right politician Joerg Haider.
On the floor of the Redoutensaal, Mr Amano and his wife swayed and twirled in time to the music.
In another corner, a young man - not from Austria - laughingly apologised to his dance partner for treading on her foot.
"Just how much real diplomacy actually goes on at a ball like this?" I asked a passing bureaucrat.
He smiled. "It is all about fostering personal relationships," he said.
"And when in Vienna, why not do as the Viennese do?"
How to listen to: From Our Own Correspondent
BBC Radio 4: Saturdays, 1130. Second weekly edition on Thursdays, 1100 (some weeks only)
BBC World Service: See programme schedules
Story by story at the