Pope Francis on Thursday marked the first anniversary of his election in prayer and quiet contemplation of the meaning of Lent, far from the adoring crowds and controversies of Rome.

In keeping with Francis's tendency to eschew much of the pomp and ceremony associated with his role, the anniversary was not marked in any official way, with the exception of a solitary tweet from the official @Pontifex account.

"Please pray for me," the 77-year-old wrote to his 12 million followers in nine languages, echoing an appeal he made in his first address to followers from the balcony of St Peter's Basilica exactly one year ago.

Francis was spending the day on a pre-Easter spiritual retreat in the Castelli Romani, a picturesque area on the southeastern outskirts of Rome.

He left the Vatican on Sunday after his weekly blessing and will return on Saturday.

The Lenten retreat is a regular fixture in the Vatican calendar and its focus on self-denial, penance and repentance chimes with the tone Francis has set for his papacy through his emphasis on the themes of mercy, humility and support for the poor.

"He did not want anything different from usual," said his spokesman, Father Federico Lombardi. "It is his way to be solemn and to insist on prayer."

The Argentinian pope's extraordinary popularity has helped increase church attendance around the world but it has also fuelled the growth of a cult of personality that he has denounced as inappropriate.

"Portraying the pope as a kind of superman, a type of star, it seems offensive," Francis recently told Italian daily Corriere della Sera.

More than anything, the pope's first year in office has been marked by his apparently sincere determination to maintain the kind of simple lifestyle the former Jorge Mario Bergoglio has had throughout his career as a priest.

- Two popes, no discord -

The pontiff lives simply in a three-room apartment rather than a papal palace. The golden cross and red cape of his predecessor have been left unworn and he is reported to regularly phone an 80-year-old widow who recently lost her son. "She is happy and I get to be a priest," he said of those calls.

That attitude has helped to fuel his popularity around the world. If retweets are counted, it is likely more Twitter users are reading what he has to say than tweets by US President Barack Obama.

The micro-blogging site was awash Thursday with commentary on the anniversary, well-wishers hugely outnumbering detractors.

"What a year it has been," tweeted Irish priest Rory Coyle while the Washington Post hailed: "A triumphant 1st year."

Amid all the plaudits, the issue of who exactly the new pope is and what he stands for remains the subject of much discussion, and the controversies he inherited have not gone away.

Allegations that he is a "Marxist" pope may be exaggerated, but there is no doubt that he is no fan of globalisation, which he once described as a "way to enslave nations."

In that sense, he seems to be a pope for these times of uncertainty and economic insecurity.

Critics and victims' organisations say he has done nothing to seriously address the issue of paedophile priests.

"He's warm and popular but he ignores the Church's greatest and ongoing crisis - the cover-up of horrific clergy sex crimes," David Clohessy, Executive Director of the US-based SNAP network of survivors of clerical abuse, told AFP.

Francis rebuffed such criticism last month, insisting the Church has been as transparent as any other institution in its handling of a problem that concerns all of society.

Francis has made waves with his determination to reform the Vatican's structures and initiate new approaches on contentious issues such as the Church's attitude to divorce and homosexuality.

Church sources say traditionalist Cardinals are resisting Francis's lead at a time when cost-cutting measures are causing disquiet within the Vatican walls.

Papal staff are fearful for their posts, already having had to accept cuts in their income because of a crackdown on overtime.

Andrea Tornielli, of Italy's La Stampa newspaper, knows Francis personally and acknowledges that his way of leading the Church has encountered some resistance.

"I do not believe groups have been formed. But his style, everything that can seem as desacralising the pontiff's role, the lack of distance and his accessibility, are a problem for some," said the journalist, who also runs the Vatican Insider website.

The unique situation created by Francis's predecessor Benedict XVI's decision to retire has led to speculation that the Vatican could easily slip into two rival camps headed by, respectively, the current, reforming pontiff and the conservative Emeritus Pope.

Tornielli says such theorising is wide of the mark, citing an email Benedict sent him last month describing the suggestions as "absurd speculation" and voicing his "profound friendship" for the man who succeeded him.