Pope Benedict XVI speaks to his cardinals during a farewell ceremony in the Clementine Hall of the Vatican's Apostolic Palace on February 28, 2013 in Vatican City, Vatican. (Photo by L'Osservatore Romano)

Pope Benedict XVI attends a meeting with his cardinals during a farewell ceremony in the Clementine Hall of the Vatican's Apostolic Palace on February 28, 2013 in Vatican City, Vatican. (Photo by L'Osservatore Romano)

Pope Benedict XVI speaks to his cardinals during a farewell ceremony in the Clementine Hall of the Vatican's Apostolic Palace on February 28, 2013 in Vatican City, Vatican. (Photo by L'Osservatore Romano)

ROME, ITALY - FEBRUARY 28: People crowd the gallery on top of St Peter's Basilica as a helicopter carrying Pope Benedict XVI passes by on its way out of Vatican City on February 28, 2013 in Rome, Italy.  (Photo by Peter Macdiarmid/Getty Images)

Pilgrims wait for Pope Benedict XVI to wave, for the last time as head of the Catholic Church, from the window of Castel Gandolfo.  (Photo by Oli Scarff/Getty Images)

Nuns wait for Pope Benedict XVI to wave to pilgrims, for the last time as head of the Catholic Church, from the window of Castel Gandolfo where he will start his retirement.  (Photo by Oli Scarff/Getty Images)

Pope Benedict XVI walks away for the last time as head of the Catholic Church, from the window of Castel Gandolfo where he will start his retirement today on February 28, 2013 in Rome, Italy.  (Photo by Franco Origlia/Getty Images)

A general view of the main Square of Castel Gandolfo crowded with pilgrims as Pope Benedict XVI arrives, for the last time as head of the Catholic Church, at the window of Castel Gandolfo. (Photo by Franco Origlia/Getty Images)

A nun becomes emotional as Pope Benedict XVI waves to pilgrims, for the last time as head of the Catholic Church, from the window of Castel Gandolfo.  (Photo by Oli Scarff/Getty Images)

Pope Benedict XVI waves to pilgrims, for the last time as head of the Catholic Church, from the window of Castel Gandolfo where he will start his retirement today on February 28, 2013 in Rome, Italy.  (Photo by Christopher Furlong/Getty Images)

A general view of the main Square of Castel Gandolfo crowded with pilgrims as Pope Benedict XVI arrives, for the last time as head of the Catholic Church, at the window of Castel Gandolfo.  (Photo by Franco Origlia/Getty Images)

Members of the Swiss Guard close the doors to Pope Benedict XVI's residence in Castel Gandolfo as he starts his retirement.  (Photo by Oli Scarff/Getty Images)

Members of the Swiss Guard prepare to close the doors to Pope Benedict XVI's residence in Castel Gandolfo and transfer responsibility for his security to the police as he starts his retirement. (Photo by Oli Scarff/Getty Images)

Swiss Guards offically close the gates of Castel Gandolfo which symbolises the end to Pope Benedict XVI's time as head of the Catholic Church and he becomes Roman Pope Emeritus on February 28, 2013 in Rome, Italy. (Photo by Christopher Furlong)

People gather together in St Peter's Square to follow the departure of Pope Benedict XVI on February 28, 2013 in Vatican City, Italy. (Photo by Carsten Koall/Getty Images)

VATICAN CITY, VATICAN - FEBRUARY 28: Night falls on St Peter's Square on February 28, 2013 in Vatican City, Vatican. The Pontiff has flown to Castel Gandolfo where he ceased to be Pope. (Photo by Peter Macdiarmid/Getty Images)