Pope Leo will travel to Monaco, the semi-enclave famous for casinos and superyachts, on Saturday on his first European trip since being elected pontiff, causing bemusement among some Vatican observers, not least because it comes 488 years after the last papal visit.

Leo will travel from the Vatican by helicopter for the one-day trip, and will be greeted at Monaco’s heliport by Prince Albert and his wife, Princess Charlene, before being taken to the palace, which has been the residence of the Grimaldi dynasty since the 13th century. It is the first time a pontiff has visited Monaco since Pope Paul III in 1538.

Matteo Bruni, the Vatican’s spokesperson, said Monaco was a “small country with big horizons” and would provide Leo, who was elected as the Catholic church’s first US pope in May last year, with his first opportunity to talk to all of Europe.

Speaking to journalists before the trip, Bruni recalled the biblical image of “the small playing a significant role”, while describing Monaco – the second-smallest state in the world after the Vatican – as a “laboratory of peace” owing to its “responsible” use of wealth and influence.

After a private meeting with Albert, Leo will head to Monaco’s cathedral in the popemobile before celebrating mass at the Stade Louis-II.

Monaco may be very wealthy, but it is also very Catholic. It is one of the few European countries where Catholicism is the official state religion, and the number of Catholic churches – five – outnumbers casinos by one, alongside the cathedral.

Albert recently refused a proposal to legalise abortion, citing the important role Catholicism plays in Monaco. Bruni said “the defence of life” would be one of the themes of the pope’s visit, while emphasising Leo’s focus would be on the wider context of defending all life, including in wars.

About 15,000 Catholics are expected to congregate for the mass, many flocking across the border from Italy. Although entrance to the stadium for the mass is free, attenders have had to pre-book. Nice-Matin, a French regional daily, reported long queues of people waiting in the rain to collect their wristbands for the event. The anticipation of Leo’s arrival goes “beyond mere curiosity”, the newspaper wrote, adding that “residents hope for a rare and deeply personal moment of communion with the pontiff”.

Albert invited Leo to Monaco when he visited the Vatican in January.

“Nobody has really been able to understand why he chose Monaco – it’s the Vatican’s best-kept secret,” said Marco Politi, a Vatican journalist. “But it’s probably a gesture of delicacy towards very small European countries. So maybe we can expect him to go to Andorra and Liechtenstein too.”

Severina Bartonitschek, the Vatican correspondent for KNA, a Catholic news agency in Germany, said Monaco was an unusual choice, especially given trips made by his predecessor Francis, known as “the pope of the peripheries”, tended to focus on marginalised, neglected areas.

“Monaco is the exact opposite,” she added.

But along with heading the two smallest states in the world, Leo and Albert share a few things in common. “They are both very Catholic, very pro-life and they both like sport,” said Bartonitschek. “Monaco is a small state but with an international community and lots of Catholics. Plus, it is doable in a day.”

Leo’s first overseas trip was to Turkey and Lebanon in November and in April he will make a 10-day visit to Africa.

He received an invitation to the White House from the US president, Donald Trump, soon after being elected pope, but has not yet taken it up. “He will eventually go, but he doesn’t want to give the impression of giving precedence to his own country, so he will prioritise other countries,” said Politi.