US President Donald Trump is due to hold talks with Pope Francis and Italy’s top leaders in Rome on the third leg of his first overseas trip.
Mr Trump and the pontiff have already clashed at a distance on issues including migration and climate change.
Mr Trump will also meet Italy’s president and prime minister, before flying to Brussels for a Nato summit.
He earlier vowed to help Israelis and Palestinians achieve peace, as he ended the Middle East leg of his tour.
The US leader began his foreign trip with a two-day stop in Saudi Arabia over the weekend, urging Muslim countries to take the lead in combating radicalisation.
Mr Trump is expected to meet Pope Francis at 06:30 GMT, before holding talks with Italian President Sergio Mattarella and Prime Minister Paolo Gentiloni.
It is hard to think of two more contrasting characters than Pope Francis and President Trump.
On one hand, the Jesuit who has made his mission the championing of the poor and dispossessed; on the other the property developer who has championed getting rich, and surrounded himself with billionaires in his cabinet.
And though this will be their first meeting they’ve already sparred. During the election the Pope on a visit to the Mexico-US border said that people who only think of building walls instead of bridges were not Christian. Donald Trump described those comments as disgraceful, and accused the pontiff of being a pawn of the Mexican government.