Before, the pilgrims were orderly and polite, subdued by suspense and unyielding rain. After, complete mayhem as it became clear that white smoke was billowing from the Sistine Chapel chimney.
Nuns threw their hands in the air, tears rolling down their cheeks, and chants of "Long Live the Pope" thundered across the cobblestoned piazza.
Complete strangers hugged, overwhelmed by emotion. A young woman sobbed uncontrollably, barely able to stand. "Mamma Mia, we have a pope!" cried Italian nun Sister Eugenia. "We have a holy father!"
The election of Argentina's Cardinal Jorge Bergoglio as the first pope from the developing world touched off a wave of jubilation in the storied square where popes have greeted the faithful for centuries. Many had been expecting a drawn-out conclave due to swirling talk of divisions among cardinals tasked with electing the pope, following the shock resignation of Benedict XVI.
But Bergoglio — who took the name Pope Francis — was elected with startling speed after five rounds of voting over two days.
"I can't explain how happy I am right now," said Ben Canete, a 32-year-old Filipino, jumping up and down in excitement.
Amid joy, there was also the usual dose of confusion — although this time it wasn't over the color of the smoke that has befuddled chimney watchers in conclaves past.
A group of Filipino visitors were overjoyed, convinced that the new pope announced by the cardinal on the loggia of St. Peter's Basilica was their countryman, Cardinal Luis Antonio Tagle.
It didn't matter much when they found out it wasn't.
"I really don't know him, but it doesn't matter. We have a new pope," said Marben Moralias from the Philippines. "God surprised us.
Argentines in the crowd went blank-faced with amazement. "I can't believe it," said one woman from Bergoglio's home country.
After the white smoke billowed, the crowds went wild as the Vatican and Italian military bands marched through the square and up the steps of the basilica, followed by Swiss Guards in silver helmets and full regalia.
They played the introduction to the Vatican and Italian anthems and the crowd, which numbered around 100,000, joined in, waving flags from countries around the world.
Catholics and non-Catholics alike were swept up in the excitement, including Elizabeth Asher, a 21-year-old Jewish student at the American University of Rome.
"It was so wonderful to see how happy everyone was," said Asher, of Montclair, New Jersey. "They were cheering 'papa, papa.' They probably didn't even know who he is, but they were just so happy to have a new pope."
It took a moment of silent prayer led by the new Pope Francis himself to get everyone to calm down. As he bent his head humbly after asking for the prayers of the faithful, the square packed with people from around the world suddenly went silent in reverence.
Then, as the crowd streamed out of the square, the celebrations continued.
"I'm so happy because the new pope is from Latin America. That means we are a big people," said Maggy Pena, a 45-year-old immigrant from the Dominican Republic. "For the first time we have a pope. And next we will have an American president. You'll see!"
AP photographer Emilio Morenatti contributed to this report.