Pope Francis was due on Friday to be handed Germany's prestigious Charlemagne Prize, given each year to public figures who have made "exceptional" contributions to the cause of promoting European unity.
Francis, a vocal champion of migrant rights and other social justice causes, is being honoured for acting as Europe's "voice of conscience," the awarding committee said when it made the decision in November.
In a break from custom, the prize is being awarded in the Vatican, rather than in the German city of Aachen. German Chancellor Angela Merkel, European Union leaders and European Central Bank President Mario Draghi travelled to Rome for the special occasion.
Francis was due to make a speech on his vision for Europe. When he last approached the topic, visiting the European Parliament in 2014, he disparagingly described the continent as a "grandmother, no longer fertile and vibrant."
Aachen Mayor Marcel Philipp, European Commission President Jean-Claude Juncker, European Council President Donald Tusk and European Parliament President Martin Schulz were also scheduled to speak during the 90-minute ceremony starting at noon (1000 GMT).
Merkel, a Protestant, was earlier in the day due to attend Mass in St Peter's Basilica celebrated by German Cardinal Walter Kasper, and to meet privately with Francis. On Thursday, the German leader held talks with Italian Prime Minister Matteo Renzi.
Argentine-born Francis, the first non-European pontiff in 13 centuries, is not the first Charlemagne Prize laureate among popes. In 2004, John Paul II was awarded the Extraordinary Charlemagne Prize, the only of its kind to date.