Tourists and pilgrims from all over the world huddled under umbrellas or took shelter under the giant pillared walkways.
And the long and wet wait was worth it as anticipation turned to prayer and celebration as Pope Francis appeared on the balcony.
Among the Irish folk with extra special reasons to travel to Rome for the conclave was Kitty Mulligan, sister of All-Ireland primate Sean Brady, the sole Irish prelate taking part in the events unfolding in the Sistine Chapel.
Kitty, a former teacher, said that her brother "was very aware of the significance of how important it (the conclave) is. It's been described as a sacred task, and that's what it is".
Cardinal Brady was in St Peter's Square for the election of Paul VI. "He would never, ever in his wildest dreams, think that he would be taking part in the conclave," she said.
Belfast priest Fr Tim Bartlett was also attending his first conclave.
Speaking before the decision was made, he said: "I believe that the man God wants at this moment in time will be chosen."
He had escorted Cardinal Brady to the Santa Marta residence on the morning of the start of the conclave. "He had a very real sense of privilege, and also felt the weight of responsibility on his shoulders," he said.
Fr David Brough, parish priest in Oldbawn, Tallaght and Bohernabreena in Dublin, and his friend Stephanie Dardis from Leopardstown, were wandering about the Square. He said: "We arrived last night, it was a spontaneous decision to come to Rome for such a historic occasion."
Soaking up the mood were Killarney couple Ella and Gary Stack. "We'd planned a trip to Barcelona but came to Rome instead when they announced the date of the conclave," She said. "There's a great feeling."
Gary had never attended St Peter's during a conclave before, but in 1979 was one of four people who had a 40-minute private audience with John Paul II.
"I was in Rome with a couple of seminarian friends when Tomas O Fiach got the red hat and we were invited to the Pope's private apartments.
"I'm a doctor, and he spoke to me about his own brother who was a doctor," he said.
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