Francis thrilled the crowd at the start of the Mass by taking a long drive about through the sun-drenched piazza and getting out of his vehicle to bless a disabled man.
It was a gesture from a man whose short papacy is becoming defined by such spontaneous forays into the crowd and concern for the disadvantaged.
Six sovereigns, U.S. Vice President Joe Biden and other leaders as well as heads of many other faiths were among the 130 delegations on the steps of the famous basilica.
Blue and white flags of Francis’s native Argentina fluttered above the crowd, which Italian media estimated could reach one million but appeared to be significantly fewer.
Pope Francis waves to crowds as he arrives to his inauguration Mass in St. Peter's Square at the Vatican
Pope Francis reaches out to pat a baby as he is driven through the crowd prior to his inaugural Mass, in St. Peter's Square
Nuns line up for the inaugural Mass of Pope Francis, at St. Peter's Square at the Vatican
Pope Francis reaches out to touch a child as he arrives to his inauguration Mass in St. Peter's Square at the Vatican
Visitiors wave flags from Germany and Argentina in Vatican square before the inauguration of Pope Francis in St. Peter's Square at the Vatican
Pope Francis speaks to the crowd in St. Peter's Square from the window of his residence before the Angelus prayer at the Vatican
Pope Francis waves upon his arrival in St. Peter's Square for his inaugural Mass, at the Vatican
A prelate stands in between rows of seats prior to the inaugural Mass of Pope Francis, in St. Peter's Square at the Vatican
Pope Francis waves to crowds as he arrives to his inauguration Mass in St. Peter's Square at the Vatican
Nuns of the Sisters of the Company of the Cross, from Spain, wait near St. Peter's Square for the start of Pope Francis' inaugural Mass, in St. Peter's Square at the Vatican,
A priest adjusts chalices on an alter before the inauguration of Pope Francis in St. Peter's Square at the Vatican
Argentina's President Cristina Fernandez arrives to attend Pope Francis' inaugural Mass in St. Peter's Square at the Vatican
Dutch Prince Alexander, second left, his wife Princess Maxima, left, Prince Felipe of Spain, right, and his wife Princess Letizia stand in St. Peter's Square for Pope Francis inaugural Mass, at the Vatican
Pope Francis holds his pastoral staff prior to celebrating his inaugural Mass, in St. Peter's Square at the Vatican
Pope Francis waves to crowds as he arrives to his inauguration Mass in St. Peter's Square at the Vatican
Pope Francis waves to crowds as he arrives to his inauguration Mass in St. Peter's Square at the Vatican