Pope Benedict delivered an emotional last Sunday prayer in St Peter's Square, saying God had told him to devote himself to prayer but assuring supporters he would not "abandon" the church.
Casting a shadow over his appearance, however, were allegations of "inappropriate behaviour" by Britain's most senior Catholic cleric, Cardinal Keith O'Brien.
Tens of thousands of supporters turned out for the historic prayers ahead of the pope's formal resignation on Thursday, often interrupting the pope with their clapping, cheering and chanting.
"The Lord is calling me to climb the mountain, to dedicate myself even more to prayer and meditation. But this does not mean abandoning the church," the pope told the crowd from the window of his residence in the Apostolic Palace in the Vatican.
"If God is asking me to do this it is precisely so I can continue to serve with the same dedication and love as before but in a way that is more appropriate for my age and for my strength."
The 85-year-old leader of the world's 1.2 billion Catholics has said he will step down because he no longer has the strength of mind and body to carry on.
His shock resignation ended an eight-year pontificate dominated by sex abuse scandals involving priests and countering rising secularism in the West.
He thanked the crowd with a final unscripted call, telling them: "We will always be close!"
The Vatican and Rome police estimated the numbers at more than 100,000 people.
"I have come to support the pope and to ask for his blessing," said Joao-Paulo, a 26-year-old trainee priest from Brazil who came with fellow seminarians.
Benedict will be only the second pope to resign of his own free will in the Church's 2,000-year history, and the first to do so since the Middle Ages.
In Britain, O'Brien, a cardinal expected to take part in the conclave to choose the next pope, rejected allegations that he had behaved in an "inappropriate" way with other priests.
The Observer newspaper said the 74-year-old archbishop of St Andrews and Edinburgh, who is known for outspoken views on homosexuality, had been reported to the Vatican over allegations stretching back 30 years.
"Cardinal O'Brien contests these claims and is taking legal advice," his spokesman said.
Three priests and a former priest, from a Scottish diocese, complained to the Vatican and demanded O'Brien's immediate resignation, adding they wanted the conclave to choose Pope Benedict's successor to be "clean".
Additional reporting by Reuters