Pope Francis’s selection was conveyed in the centuries-old way, with the puffs of white smoke billowing above St. Peter’s Square in Vatican City. Eighteen months later, this pontiff has 23 million Twitter followers who have made him the most retweeted leader in the world.

His unexpected social media stardom is catapulting the antiquated communications culture of the Vatican into the modern digital world, upending its telegraph office, preference for snail mail and a daily schedule that includes virtually everyone in the Vatican’s information infrastructure clocking out at midday for a long Italian lunch.

And the success of his pastoral directness online is prompting some soul-searching about what is an appropriate digital persona for a descendant of Peter. Should a Holy Father follow others? (For now, @Pontifex follows only himself — the official papal accounts in nine languages.)

Should he communicate directly to his flock?

Can he and his social media team project a higher authority that keeps the Holy See parted from the coarse culture and smut of the Internet? And when there are incursions, how should the pope deal with trolls?

For now, he ignores them. And the Vatican has sketched out some other basic rules.

Among them: Promote Jesus, not Francis — trickier than it looks when smartphone photos of him hugging people and tales of him cold-calling ordinary Catholics go bananas on Twitter, Instagram and Facebook.

Speaking of Facebook — no Facebook. Facebook is too two-way, too social of a social medium for the leader of the world’s largest church. Vatican communication strategists aren’t sure they want a Francis page where the pope could be friended, and what would happen if the who-am-I-to-judge pope didn’t respond to his friends? The thumbs-downs could be devastating.

Don’t focus too much on the United States, a superpower this humble pontiff has made clear he thinks receives enough attention, a strategy likely to be in place this week when Francis makes his first trip to the United States.

“It’s only recently [that] the scope of what this possibly could mean for the church has really started to affect people’s thinking,” said Bryan Crable, a communications professor at Villanova University. He has been sending students of the Catholic college outside Philadelphia to intern at the Vatican for a decade, where they sometimes serve as millennial guides to topics such as Instagram (yes) and Snapchat (no).

Crable noted that the Pontifical Council for Social Communications, which functions as the Vatican’s think tank and training arm on communications, was created decades ago to give Catholics a guide to what movies they should and shouldn’t see.

“I think they are moving from an approach that sees contemporary media as a source of contamination to an understanding that there are ways in which contemporary communications technology allow for a different way of engaging with people of faith, both within and outside the Catholic Church,” he said. “To approach it not simply as: ‘What are things that are harmful?’ but what opportunities might be there for the church to engage people, like, what is the pope doing about issues of social justice?”

For a man who says he doesn’t know how to use a computer and hasn’t watched television since the 1970s, Francis has a remarkably digestible, punchy online style.

In June, the day he released a major climate change document, Francis shared this:

In September 2013, he tweeted this, as world leaders contemplated military action on Syria:

Many of his tweets, however, are purely spiritual, such as this one from June 2013:

Despite the huge success of @Pontifex, started modestly by Pope Benedict in December 2012, it’s not a simple task to modernize Vatican communications.

Francis brought in a former chairman of the BBC to recommend an overhaul of the Vatican’s archaic communications operation. Lord Patten concluded it would be “beyond bizarre” for the Vatican to keep its “eyes closed to the way every other media organization is managed in the second decade of the 21st century.” Francis also brought in McKinsey Consulting.

“Our objectives were ‘to adapt the Holy See media to changing media consumption trends, enhance coordination and achieve, progressively and sensitively, substantial financial savings.’ ” Patten said in a talk in the spring.

That means streamlining the dozen communications fiefdoms that compete with one another and duplicate efforts. They include the Vatican’s newspaper, radio and TV as well as a media office whose “spokespeople” have little access to Francis himself, a telegraph office and an Internet office that will not consider interactive chats and says actual paper letters — not e-mail — “is still the preferred format” for papal missives, its director, the Rev. Lucio Adrian Ruiz, a priest from Argentina, told Italy’s La Stampa newspaper.

The new prefect, or head, of the Secretariat is Dario Edoardo Viganò, an Italian cinema expert whose selection is seen as an acknowledgment that Francis understands the power of image. A claim to fame was Viganò’s dramatic — and very European — staging of the 2013 exit of Benedict, who became the first pope to retire. Benedict was carried by a helicopter away from St. Peter’s, a re-creation of the opening scene of the film classic “La Dolce Vita,” in which a helicopter carrying a statue of Jesus to the Vatican hovered over the city, seeming to bless it, as did the image of a parting Benedict.

Some longtime watchers of Vatican communications say just getting the bureaucracy modernized is an example of Francis’s success in cutting through the Curia’s entrenched red tape. However, the new leadership is made up of priests from inside that same bureaucracy; their résumés aren’t typical of people running major 21st-century newsrooms.

“Too much magenta and too many collars,” said a communications expert who works with the Vatican often and spoke on the condition of anonymity.

All this aside, the Vatican in some ways has been an innovator in communications.

It has been online since the mid-1990s and set up a YouTube channel around 2008 — just a few years after the video-sharing site was started. The Vatican’s Instagram feed, with more than 25,000 followers, shows Pope Francis kissing babies, washing people’s feet and twirling a basketball on his finger with the Harlem Globetrotters.

And Catholic media are considered leaders in the institutional faith world when it comes to creative efforts in satellite radio and podcasting, including EWTN and the Catholic Channel.

The Vatican’s largest media arm is its radio operation.

But @Pontifex is by far its most visible.

There are nine @Pontifex handles, offering the same tweets in different languages. Spanish and English are the largest, followed by others including Arabic and Latin, which is a sleeper social media hit with 390,000 followers (and a translator who gained some celebrity himself for translating the children’s book “Diary of a Wimpy Kid” into Latin).

Despite the reach of @Pontifex, the account doesn’t have a full-time employee. Michael O’Loughlin, who covers the church for the Catholic site Crux and is the author of “The Tweetable Pope,” said about half a dozen people across different departments contribute in an informal way to the powerhouse account.

Spoiler alert: Francis doesn’t actually tweet, O’Loughlin says. He picks the themes he wants the account to focus on in a given week, often to reinforce his sermons and major addresses, O’Loughlin says, and he signs off on the tweets.

A key fact about @Pontifex is that it’s housed in the secretary of state’s office.

“They see [that] Twitter — and social communications — are a diplomatic tool,” O’Loughlin said. “It’s a way to reach 23 million followers, but also influential Catholics, leaders — to get the pope’s message out.”

And once the message is out? Like any other major institution, the Vatican is struggling with the often superficial nature of online interaction and trying to figure out whether retweets can foment action and real change.

“You have a lot of skepticism whether this is for the most part in some ways creating a passive understanding of social change,” Crable said.

Villanova senior Melissa Connolly, 21, interned last semester at the Pontifical Council for Social Communications.

“The big thing is he’s not on Facebook,” she said of the pope. “We asked about it because, like a billion people have it, and the pope isn’t one of them. They said they didn’t see a real use for it because Facebook is more to connect and they didn’t think you could ‘connect’ with the pope over social media.”

The type of “connection” you have on Facebook with someone isn’t “authentic enough,” she recalled them saying. “If you’re going to connect with [Francis], it should be more in a spiritual sense, and it’s hard to create that online.”

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