Pope Leo XIV heads to Monaco on Saturday for a one-day visit that will see him greet the Catholic faithful in a Mediterranean principality known best for yachts and gambling.

The decision to choose tiny Monaco for the US-born pope's first trip in Europe since his election last year has caused puzzlement among observers.

Wedged between the mountains and the sea on the French Riviera, Monaco is the world's second-smallest state after the Vatican, and resolutely Catholic.

Ties between the two states date back to the Middle Ages and they share interests such as promoting interfaith dialogue and environmental protection.

Yet many commentators question why he is making the eight-hour trip, his second abroad after visiting Turkey and Lebanon in a joint visit last year.

Philippe Orengo, Monaco's ambassador to the Holy See, said the pope was interested in visiting a country where there has been a resurgence in Catholicism in recent years.

The pope "wanted to see for himself what is happening in Monaco, where this movement of renewal is based on an embraced faith, and on an inclusive popular piety and devotion," he told AFP.

In the first papal trip to Monaco in modern times, Leo will meet Prince Albert II and take a tour in his popemobile, before holding a mass in the local stadium.

Large crowds are expected from among Monaco's 39,000 inhabitants as well as surrounding France.

But so far the discreet American has drawn less fervour than Argentine reformer Pope Francis, who died last April after leading the world's 1.4 billion Catholics for 12 years.

'Ethics and money'

Monaco is steeped in Catholic tradition and -- rare among most of Europe -- abortion remains illegal there.

However, abortion has been decriminalised, and women who head across the border to France are not prosecuted.

As a tax haven that made its money in casinos and where prostitution is legal, Monaco is not everybody's idea of a Catholic state.

It is a somewhat incongruous location for a visit by Pope Leo who, like Francis, has prioritised the poor and marginalised.

In an interview published Wednesday, Prince Albert said Catholicism "is one of the elements that contributes to Monaco's unique character", as well as to his own identity.

"Of course, the balance between ethics and money is never easy," he told French Catholic daily La Croix.

"But perhaps the question isn't really about wealth itself, but about how it is used... The Principality, through its various associations and institutions, is very generous," he added.

He said it was an "immense honour and a great joy" to host the pope.

"One of Monaco's distinctive features is a kind of positive secularism, which recognises the legitimate autonomy of the spiritual and temporal spheres," added Guillaume Paris, a senior clergyman in Monaco.

"We talk to each other, we know each other, we recognise each other," he told AFP.

Diplomatic niceties

The pope will arrive by helicopter, a diplomatic subtlety that spares him from landing on French soil without actually visiting France.

He will then visit the princely palace, the official residence of the Grimaldi dynasty since the 13th century, for a private meeting with Prince Albert.

The two men share a concern for ecology, with the prince emphasising in his interview "the spiritual dimension that the Church brings to this struggle" to protect the environment.

They also share a passion for sport, according to the diocese of Monaco. Leo, 70, swims and plays tennis regularly.

The highlight of the visit is expected to be an open-air mass at 1430 GMT at the Louis II Stadium where around 15,000 people are expected.

A heavy security and logistics operation is in place, comparable to that put in place for the Monaco Grand Prix.