A smiling Pope Benedict XVI looked relaxed on Wednesday as his white "popemobile" bore him through the famous plaza where more than 150,000 people had gathered under a bright, cloudless sky for his historic sendoff.
A woman clutching a rosary wiped away tears as the octogenarian Benedict passed. One of the hundreds of cardinals and bishops in their red and purple-sashed robes could also be seen tearing up.
Some in the throng held up huge banners with messages such as "Benedict, we'll miss you!" and "The pope is the heart of this city!" or waved the Vatican's yellow and white flag at the pontiff's last public event.
A hush fell over the sea of pilgrims as the pope began speaking.
Benedict drew an analogy between his reign and a miracle recounted in the Bible when Jesus Christ calmed the waters as he was sailing on a fishing boat with his disciples including St Peter -- who is believed by Christians to be the first pope.
"The Lord gave us days of sun and of light breeze, days in which the fishing was good. There were also moments when there were stormy waters and headwinds... as if God was sleeping," the pope said in an apparent reference to the multiple scandals that have plagued his reign.
"But I always knew that God was in that boat and I always knew that the boat of the Church is not mine, is not ours, but is his and he will not let it sink," the leader of the world's 1.2 billion Catholics told the cheering crowd.
"I never felt alone," he said.
Benedict also said his decision to resign -- which makes him the first pope to do so since the Middle Ages -- had not been an easy one but had been taken for the good of the Church.
"I took this step in full awareness of its gravity and novelty but with profound serenity of spirit," he said, adding: "I will continue to accompany the Church with prayer and reflection."
The frail 85-year-old stunned the world with his abrupt decision to end an eight-year reign dogged by scandal and Vatican infighting, declaring he was too weak to keep up with the modern world.
The scourge of paedophile priests and cover-ups by their superiors cast a dark shadow over Benedict's papacy, combined with a longstanding money-laundering scandal at the Vatican bank, which exposed infighting among Benedict's closest allies.
What observers said may have been the last straw was the scandal that came to be known as "Vatileaks", in which his trusted butler leaked secret papal memos revealing intrigues between rival groups of cardinals.
But Wednesday's crowds did not dwell on the scandals.
"I have come in gratitude for everything he has done these past eight years," said Father Giulio, a 67-year-old priest from the Abruzzo region.
"Resigning is a powerful message for every Christian. He resigned without bitterness but instead in sweetness and serenity," he said.
Giuseppe Fan, a Vietnamese seminarian, stood on tiptoe on the steps of one of the square's fountains for a better view.
"I love the pope," he told AFP. "I'm sad that he's leaving, but he has made a grand gesture of love for the Church."
Benedict's resignation is a break with Catholic tradition that has worried conservatives but kindled the hopes of Catholics around the world who want a successor who will breathe new life into the Church.
Sharon Clark, a tourist from the United States, told AFP: "I admire Benedict, but I hope the next pope will have the strength to unite the Church and help it grow again -- and bring back a bit of morality."
While most appeared to accept the pope's imminent departure, at least one banner pleaded: "Benedict, change your mind!"
But Jan Graubner, archbishop of Olomouc, Czech Republic, said that while he was sad to see the pope leave, "gratitude outweighs sadness because I see that the Holy Father wants this. It's his will."
Benedict told English-speaking pilgrims he was "deeply grateful for the understanding, support and prayers of so many of you, not only here in Rome, but also throughout the world."
Later Wednesday the pope followed up his farewell speech with what the Vatican said would be one of his last Tweets: "If only everyone could experience the joy of being Christian, being loved by God who gave his Son for us!" the pope wrote.
The Vatican has said Benedict will receive the title of "Roman pontiff emeritus" and can still be addressed as "Your Holiness" and wear the white papal cassock after he officially steps down at 1900 GMT on Thursday.
Rome has been gripped by speculation over who the leading candidates might be to replace him -- the so-called "papabili" -- as cardinals from around the world fly in ahead of the conclave to elect the next pope.
Rumours and counter-rumours in the Italian media suggest cloak-and-dagger lobbying, prompting the Vatican to condemn what it has called "unacceptable pressure" to influence the papal election.
Campaign groups have also lobbied the Vatican to exclude two cardinals accused of covering up child sex abuse from the upcoming election conclave.
A total of 115 "cardinal electors" are scheduled to take part in next month's conclave to choose a successor to Benedict.