Pope says he's resigning for the 'good of church'

The audience was the start of a busy day for Benedict: he will also preside over Ash Wednesday services later in the day to mark the official start of the Catholic Church's solemn Lenten season. The service is usually held in a church on Rome's Aventine hill, but was moved at the last minute to St. Peter's Basilica. The Vatican said the shift was made to accommodate the crowds, though it will also spare the pope the usual procession to the church.

The Vatican insisted no serious medical ailment was behind Benedict's decision to retire, though it admitted for the first time on Tuesday that Benedict has had a pacemaker for years and recently had its battery replaced.

The move sets the stage for a conclave of cardinals by mid-March to elect a new pope.

"It is the perfect occasion to give a cordial and affectionate goodbye to this pope who has given us a great example of courage, humility, inner honesty, and a great love for the church," said Monsignor Claudio Maria Celli, head of the Vatican's communications office.

Follow Nicole Winfield at www.twitter.com/nwinfield

Trisha Thomas and Daniela Petroff contributed to this report.