Tens of thousands of people — family, friends and supporters of the new "princes" of the church — packed the square, waving flags from the cardinals' homelands and toting banners with their pictures on them.
During the Mass, Benedict placed a golden ring engraved with a crucifix and the papal seal on each man's right hand. The pope said the ring was a symbol of their commitment and fidelity to the church, like the rings exchanged by a bride and groom.
"May your acceptance of the ring be for you a renewal of your 'Yes,' your 'Here I am,' addressed both to the Lord Jesus who chose you and constituted you, and to his holy church which you are called to serve with the love of a spouse," he said.
The pope and new cardinals wore golden vestments that fluttered in the springtime breeze. The rest of the College of Cardinals sat off to the side of the altar in their red robes.
Benedict referred to his predecessor John Paul II during his homily Saturday, saying he was particularly devoted to Mary, the mother of Christ. Saturday is the Feast of the Annunciation — when, according to the Bible, an angel told Mary that she would bear a child.
Benedict recalled that John Paul had attributed his survival of a 1981 assassination attempt in St. Peter's to Mary's presence.
"In memory of that tragic event, he had a mosaic of the Virgin placed high up in the Apostolic Palace, looking down over St. Peter's Square, so as to accompany the key moments and the daily unfolding of his long reign," he said.
A day earlier, Benedict warmly embraced the cardinals and placed crimson hats on their heads — symbols of their elite rank and willingness to shed blood for the church.
During Friday's consistory to formally elevate the new cardinals, tears welled up in Benedict's eyes as he gripped the shoulders of Cardinal Stanislaw Dziwisz, the Polish prelate who faithfully served John Paul for 40 years.
Dziwisz, as well as churchmen from Hong Kong, Boston, Venezuela, Spain, South Korea and the Philippines, join members of the elite College of Cardinals who will choose the German pontiff's successor. They show the worldwide reach of the 1 billion-member Roman Catholic Church.
There are 193 members of the College of Cardinals, 120 of whom are under age 80 and eligible to vote for the new pope. Among the members, 140 attended the consistory to welcome the new cardinals.
The pope invited the College of Cardinals to lunch with him in a Vatican auditorium after Saturday's Mass.
Cardinal Sean O'Malley, who was brought in to clean up the Church in Boston after a major sex abuse scandal, was among the new cardinals, along with William Levada, formerly the archbishop of San Francisco and Portland, Oregon. Levada took over Benedict's old job as prefect of the Congregation of the Doctrine of the Faith, the Vatican's chief doctrinal watchdog.
The new cardinals also included Hong Kong Bishop Joseph Zen, an outspoken champion of religious freedom in China; Archbishop Jorge Liberato Urosa Savino of Caracas, Venezuela, who has sought to reduce tensions between the church and President Hugo Chavez; and Archbishop Gaudencio B. Rosales of Manila, Philippines, the Catholic bastion of Asia.