Pope Francis’ diplomatic skills are being tested in his first audience with a visiting head of state - Argentine president Cristina Kirchner, with whom he clashed over her socially liberal policies.
Ms Kirchner will call on the former Archbishop of Buenos Aires at his temporary home in the Vatican hotel on the edge of the Vatican gardens, a day before she and other world leaders attend his installation Mass in St Peter’s Square.
She and her predecessor and late husband Nestor Kirchner defied church teaching to adopt a series of measures with popular backing, including mandatory sex education in schools, free distribution of contraceptives in public hospitals, and the right for transsexuals to change their official identities on demand. Argentina was the first Latin American country to legalise same-sex marriages.
Meanwhile Zimbabwe’s president Robert Mugabe arrived in Rome for the inaugural mass.
Mugabe is the subject of a travel ban by European nations in protest at his human rights record in a decade of political and economic turmoil, but it does not affect his trips to the Vatican through Italy or United Nations meetings elsewhere.
A practising Catholic, Mugabe, 89, joined world leaders at the 2005 funeral of Pope John Paul II who visited Zimbabwe on an African pilgrimage in 1988. At the Pope’s request then, Zimbabwe suspended criminal executions but hangings resumed nearly a decade later.
Bartholomew I, the spiritual leader of the world's Orthodox Christians, will attend Pope Francis' installation Mass - the first time an ecumenical patriarch has been to a papal investiture since the churches split nearly 1,000 years ago.
The Roman Catholic and Orthodox churches were united until the Great Schism of 1054, which was precipitated largely by disagreements over the primacy of the Pope.
Francis’ predecessor, Pope Benedict XVI, had made uniting all Christians and healing the split a priority of his pontificate. A joint committee has also been working to mend the rift between the two branches of Christianity.
A spokesman for the Istanbul-based Patriarchate said the decision to attend was “the fruit” of the growing dialogue between the Roman Catholic and Orthodox churches.
Bartholomew has made several previous visits to the Vatican, including attending the funeral of Pope John Paul II in 2005. Bartholomew also hosted Benedict during a 2006 visit to Istanbul.