Pope: 'I've had moments of joy and turbulent seas'
The pope has basked in an emotional send off at his final general audience in St Peter's Square, recalling moments of "joy and light" but also times of great difficulty.
He also thanked his flock for respecting his decision to retire.
Tens of thousands of people toting banners saying "Grazie!" - "Thank you" - jammed the piazza in Rome to bid Benedict farewell and join the appointment he has kept each week for eight years to teach the world about the Catholic faith.
Benedict clearly enjoyed the crowds, taking a long victory lap around the square in an open-sided car and stopping to kiss and bless half a dozen children handed to him by his secretary.
In keeping with the historic moment, Benedict changed course and did not produce his typical professorial Wednesday catechism lesson. Rather, he made his final public appearance in St Peter's a personal one, explaining once again why he was becoming the first pope in 600 years to resign and urging the faithful to pray for his successor.
"To love the church means also to have the courage to take difficult, painful decisions, always keeping the good of the church in mind, not oneself," he said to thundering applause.
He recalled that when he was elected pope on April 19, 2005, he questioned if God truly wanted it. "'It's a great burden that you've placed on my shoulders,'" he recalled telling God.
During eight years, he said "I have had moments of joy and light, but also moments that haven't been easy ... moments of turbulent seas and rough winds."
But he said he never felt alone and thanked his cardinals and colleagues for their guidance and for "understanding and respecting this important decision."
Under a bright sun and blue skies, the square was overflowing with pilgrims and curiosity-seekers. Those who could not get in picked spots along the main boulevard leading to the square to watch the event on giant TV screens. Some 50,000 tickets were requested for Benedict's final master class, but Italian media estimated the number of people actually attending could be double that.
"It's difficult - the emotion is so big," said Jan Marie, a 53-year-old Roman in his first years as a seminarian. "We came to support the pope's decision."
With chants of "Benedetto!" erupting every so often, the mood was far more buoyant than during the pope's final Sunday blessing. It recalled the jubilant turnouts that often accompanied him at World Youth Days and events involving his predecessor, Pope John Paul II.
Benedict has said he decided to retire after realising that, at 85, he simply did not have the "strength of mind or body" to carry on. He will meet cardinals for a final time tomorrow, then fly by helicopter to the papal residence at Castel Gandolfo south of Rome.
There at 8pm the doors of the palazzo will close and the Swiss Guards in attendance will go off duty, their service protecting the head of the Catholic Church over - for now.
Many of the cardinals who will choose Benedict's successor were in St Peter's Square for his final audience.
Vatican officials say cardinals will begin meeting on Monday to decide when to set the date for the conclave to elect the next pope.
But the faithful in the crowd were not so concerned with the future; they wanted to savour the final moments with the pope they have known for eight years.
"I came to thank him for the testimony that he has given the church," said Maria Cristina Chiarini, a 52-year-old housewife who travelled by train from Lugo in central Italy with 60 members of her parish. "There's nostalgia, human nostalgia, but also comfort, because as a Christian we have hope. The Lord won't leave us without a guide."