Pope Leo XIV, the first US pontiff, made his debut tour of St Peter’s Square on Sunday in a popemobile, greeting tens of thousands of pilgrims and well-wishers ahead of his inauguration mass.
Chicago-born Robert Francis Prevost, who became head of the world’s 1.4 billion Catholics on May 8, stood in the white vehicle as it drove through cheering crowds, smiling, waving and making the sign of the cross.
US Vice President JD Vance is among the hundreds of dignitaries due to attend the inauguration mass that begins at 10:00 am (0800 GMT).
Leo will preside over the ceremony rich in rites and symbols, where he will receive his special papal ring before giving a homily that will set the tone for his papacy.
After spending two decades as a missionary in Peru, the 69-year-old is unknown to many Catholics, but during the past week he has offered glimpses of the kind of leader he will be.
In meetings with journalists, clergy and diplomats, he repeatedly called for peace in a world full of conflicts and defended social justice.
He also emphasised traditional Catholic values, including the importance of a family built around a “stable union of a man and a woman”, and defended the rights of the unborn.
Inacia Lisboa, 71, originally from Cape Verde but who lives in Rome, said she got up early to get a good spot to see a man she said had already “entered my heart”.