Behind them is the Bel Espoir, a schooner vessel on which the youths -- whether from Libya and Egypt or France and Bosnia -- have been sailing the Mediterranean to promote peace.

"For me especially it means a lot that the pope believes in the project and he wants to come and meet us," Jesus Marro, a 30-year-old Spaniard, told AFP.

"He believes in peace and building bridges together."

Since March, the ship, built in 1944 and recently restored, has welcomed some 200 young people aged 19 to 35 from different cultures and religions, making voyages across various points of the Mediterranean.

The current trip began in Naples and was headed to Marseille, the eighth and final stop.

Hailing from all parts of the Mediterranean and involved in community projects in their home countries, the youth onboard say they see the voyage as an opportunity to promote dialogue in the face of what they called a worrying rise of conflict.

On Friday afternoon, during a visit to the three-masted ship docked at the port of Ostia outside Rome, the US pope sought to encourage them to listen in "a world that is increasingly prone to violence, hatred and separation".

Greeted by singing, the head of the Catholic Church came aboard, inspected the cabins and shared pastries in the boat's small dining room.

"Today's world needs signs and testimonies that give hope more than words," he said in an impromptu speech in English on the main deck.

- 'Life is short' -

While sailing, the participants, who include Muslims, Orthodox Christians, Catholics and those without religion, help with chores such as cooking, cleaning and night shifts, providing a feeling of closeness.

Christina Hilana, a 27-year-old Palestinian from a village near Ramallah in the West Bank called the experience "very moving".

"These two years have been very painful, and leaving my country in this situation has not been easy at all," said the young woman wearing a black and white keffiyeh headdress and a gold cross around her neck.

Fatima Al-Wardi, a 30-year-old Iraqi Muslim who runs a humanitarian project in Baghdad, had never seen the sea before the voyage.

"I wasn't ready, I'm afraid of water, I can't swim, but life is short and when you get a chance, you have to take it," she said.

"Iraq has seen the American army, then civil war between Sunnis and Shiites, and now there's ISIS. We've been through many incessant conflicts, but we still need peace because we believe in humanity," she said.

- 'School of Peace' -

The project's co-organiser, Catholic priest Alexis Leproux from Marseille, said every day the youth exchange views on topics as varied as the environment, economy, role of women, education and cultural dialogue.

It is about "building a culture of encounter as an alternative to the culture of conflict and rivalry, and that can be learned", he said.

Back on land, participants continue the experience during seminars and workshops in the cities they visit as part of the Catholic Church's 2025 edition of "Mediterranean Encounters".

Al-Wardi from Baghdad shared a passage from the Koran she said had left an impression.

"'Go out, explore people. I created you all so that you could get to know each other... You just have to step outside your comfort zone'."