Pope Leo has officially assumed the role as the 267th pontiff of the Roman Catholic Church, taking part in a formal ceremony to mark the beginning of his papacy.
Some 200,000 people gathered for the two-hour papal mass in St Peter's Square.
Pope Leo takes over a Church still battling the fallout of the clerical child abuse scandal, and trying to adapt to the modern world.
He says he is aware of the challenges he takes on with this leadership role - and says he sees his task as bringing about unity.
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