Pope Francis begins his papacy in earnest today ahead of his formal inauguration mass, with a weekly prayer address used by previous pontiffs to comment on international affairs.
The pope's first Angelus prayer, delivered from a window high above St Peter's Square, is a chance for the first Latin American pontiff to begin to sketch out a more global vision for the role of the Roman Catholic Church.
City authorities are expecting around 200,000 people to turn out. The 76-year-old pope has already been winning hearts with an informal style markedly different from that of his more austere predecessor Benedict XVI.
A million people may attend the pope's inauguration on Tuesday, including world leaders who are set to begin flying into Rome today.
Among them is Argentine President Cristina Kirchner who had tense relations with the former archbishop of Buenos Aires, Jorge Mario Bergoglio, before his surprise election on Wednesday to lead the world's 1.2 billion Catholics.
US Vice President Joe Biden was also due to arrive later today.
Francis has already spoken to Catholic leaders about the need for spiritual renewal and evangelisation and cautioned them against worldly glories, as well as calling for a "poor Church" that should be closer to ordinary people.
He warned cardinals that the Church would fall apart "like a sand castle" if it did not have a solid spiritual foundation and urged them to share their wisdom -- "good wine that gets better over the years" -- with young people.
At the same time, Francis has faced accusations at home that he failed at the time to speak out against brutalities committed during the years of the military junta in Argentina (1976-1983) when he was head of the country's Jesuits.
The Vatican has firmly rejected claims that he did not intervene when two Jesuit priests were tortured by the dictatorship, saying the allegations were part of a leftist, anti-clerical campaign.
The Argentine judge who investigated the case, German Castelli, also came out in support of the pope yesterday saying that prosecutors had found that Bergoglio had "no case to answer".
But the Grandmothers of the Plaza de Mayo organisation, founded to help locate children who were kidnapped during the military era, lambasted the new pope.
"He has never spoken of the problem of people who had disappeared under dictatorial rule," said Estela Carlotto, the head of the group, whose daughter Laura was abducted and killed.