Benedict seemed touched by the outpouring of affection after his decision to go down in history as the first pontiff in some 600 years to resign. The pontiff told cardinals last week that he no longer has the mental and physical stamina to vigorously shepherd the church.
Looking into hazy sunshine Sunday, he smiled shyly at the sight of the crowd below, filled with pilgrims waving their countries' flags and holding up banners with words of support. One group of Italians raised a banner which read: "We love you."
Speaking in Italian, the pope told the cheering crowd: "Thanks for turnout in such numbers! This, too, is a sign of the affection and the spiritual closeness that you are giving me in these days." He stretched out his arms as if to embrace the faithful from across the vast expanse of the square.
Benedict made no direct reference to his departure. But in his comments to Spanish-speaking pilgrims he asked the faithful to "continue praying for me and for the nextpope."
The traditional Sunday window appearance normally attracts a few thousand pilgrims and tourists, but this time city officials prepared for as many as 150,000 people seeking to witness one of Benedict's last opportunities to connect with the masses.
Authorities also used the event as a kind of trial run for the crowds expected to flock to the square in the coming weeks for the next pope's installation.
Following tradition, Benedict's successor will make his first papal appearance by stepping onto the central balcony of St. Peter's Basilica on the square, shortly after puffs of white smoke from the Sistine Chapel chimney tell the world the cardinals have made their secret selection.