The First Spiritual Duty of the Pope francis, Leader of 1.2 billion Roman Catholics

Hundreds of thousands of people are already filling the space at St. Peter's Square and surrounding streets for the Mass to formally install Francis as the new leader of the world's 1.2 billion Roman Catholics. The crowd may be the biggest in Rome since more than 1.5 million people came to the city for the beatification of the late Pope John Paul II on May 1, 2011.

The Vatican said six sovereigns, including from Belgium and Monaco, will be among the leaders of more than 130 delegations at the Mass. One significant attendee will be Bartholomew I, the ecumenical patriarch of Orthodox Christianity, the first time a spiritual leader of world Orthodoxy will attend a papal inaugural Mass since the East-West Schism of 1054.

It will be attended by more than 30 delegations representing other Christian Churches as well as representatives of the world's Jewish and Islamic communities.

U.S. Vice President Joe Biden and other Western leaders will be in the same VIP section on the steps of St. Peter's Basilica with Zimbabwe President Robert Mugabe, who is technically infringing a European Union travel ban.

Mugabe has been banned since 2002 because of allegations of vote rigging and human rights abuses but the Vatican is not part of the European Union, allowing him to bend the rules.