Benedict XVI has marked the formal beginning of his reign as Pope by appealing for Christian unity.
In the sermon at his inauguration Mass in a packed St Peter's Square, the Pope said: "Let us do all we can to pursue the path toward the unity".
He also sent greetings to the Jewish people who he said shared a joint spiritual heritage with Christians.
He said his task was not to pursue his own ideas, but to listen to and be "guided by the will of God."
"Like a wave gathering force, my thoughts go out to all men and women of today, to believers and non-believers alike," he said, addressing the crowd of 350,000 people gathered for the open-air service in front of St Peter's Basilica.
Cheers and applause
In the most significant moment of the two-hour Mass, the Pope was presented with the Papal ring and the pallium - a narrow stole of white wool.
SYMBOLS OF POWER
Embroidered with five red crosses representing blood of Christ
Made from lambs wool signifying role as shepherd
Reserved for archbishops and popes
When worn by Pope is symbol of pontifical power
Known as the Fisherman's Ring
Made from gold
Bears image of St Peter in a boat fishing and name of Pope
Acts as papal seal
Is destroyed when Pope dies
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They are symbols of the Pope's power and his role as shepherd of the flock of 1.1 billion Roman Catholics worldwide.
After the mass, Benedict XVI, dressed in a gold robe over sacred white vestments, was driven around the crowds in St Peter's in an open white car.
Standing on the back of the vehicle the Pope waved and smiled to the gathered pilgrims, who cheered and applauded as he passed.
In centuries gone by, the new pontiff would be crowned with a special tiara and carried around the square in a wooden chair, but this ritual was abolished by Pope John Paul I.
The Pope then moved inside the Vatican to greet some of the dignitaries who had attended the service one by one.
Thousands of Germans had flocked to Rome over the past few days, eager to see a fellow countryman mount the throne of St Peter for the first time since the mid-11th century.
The Pope's elder brother, 81-year old Reverend Georg Ratzinger, also attended the inauguration along with German Chancellor Gerhard Schroeder and President Horst Koehler.
Other heads of state and government included French Prime Minister Jean-Pierre Raffarin and Spanish King Juan Carlos.
US President George W Bush was represented by his brother Jeb, the Florida Governor, who leads a delegation of 21 members of Congress.
From Britain, Prince Philip and the Archbishop of Canterbury, Rowan Williams, attended.
In his homily, as he did in the first Mass following his election as Pope, Benedict XVI also spoke of his inadequacies as Pontiff and how the prayers of others would sustain him in his task:
"I am not alone. I do not have to carry alone what in truth I could never carry alone.
"All the Saints of God are there to protect me, to sustain me and to carry me. And your prayers, my dear friends, your indulgence, your love, your faith and your hope accompany me."
Speaking of the challenge ahead of him, the Pope said he would not for now present a programme of governance to the Church.
As well as being steeped in tradition the ceremony contained new elements - in a break with previous papal installations the attending cardinals did not kneel before the Pope and pledge obedience.
Instead this ritual was carried out by a group of 12 people, chosen to represent the diversity of the Church and the 12 original apostles.
The group was comprised of three cardinals, a bishop, a priest, a deacon, a married couple, a nun, a monk and two young people who have received the sacrament of confirmation.