One Vatican watcher said Benedict's installation Mass was unprecedented for its significant use of Greek, a sign that the Pope might be striving for a historic unification with eastern Orthodox Catholics.

"I think he is going to try to do what John Paul II could not, and that's reunite Christians -- first the eastern orthodox, then the Anglicans, and then the evangelicals. He appealed to all of them in his homily," said Robert Moynihan, editor of Inside the Vatican, a respected monthly and online publication on Vatican affairs.

Once the ceremony ended the 78-year-old pontiff was driven around the square to greet visitors, and to signify hope for more than a billion Catholics as they adjust to their new spiritual leader.

Benedict XVI said that his predecessor Pope John Paul II was "at home" among the saints in heaven, but stopped short of calling for his canonization. Pope Benedict XVI pledged to pursue the will of God during his papacy and declared that "the entire host of saints" would guide him in that pursuit.