Tens of thousands of young people filled a vast field on the outskirts of Rome to see Pope Leo, in the largest event yet of the new Catholic pontiff's tenure.
It forms part of a special weekend aimed at energising Catholic youth.
Young people from more than 146 countries were pressed against fences in the Tor Vergata field as Pope Leo toured the crowd in his white popemobile in late afternoon.
The pope, smiling broadly, waved, offered blessings and occasionally caught small stuffed animals and national flags thrown by the youth as he passed by.
"Dear young people ... my prayer for you is that you may persevere in faith, with joy and courage," Pope Leo said in remarks later to the crowd.
"Seek justice in order to build a more humane world," he said.
Adding: "Serve the poor, and so bear witness to the good that we would always like to receive from our neighbours."
Many of the youth attending the event spent all day waiting in the field in heat approaching 30C.
Organisers used water cannons to help cool down people in the crowd.
"For me, it is an incredible emotion because I had never been to an event like this before," said Maya Remorini, from Italy's Tuscany region. She said her group had arrived around 5am that morning.
Many of the youth are expected to sleep in the field overnight, waiting for a second chance to see Pope Leo tomorrow morning, when the pope is due to celebrate a Catholic mass.
The weekend events are tied to the ongoing Catholic Holy Year, which the Vatican said has attracted some 17 million pilgrims to Rome since it started at the end of 2024.
Pope Leo, the first US-born pope, was elected on 8 May by the world's cardinals to replace the late Pope Francis.
