At one end of the correspondence: His Holiness, Francis, Vicar of Christ, Pope of Rome. At the other: Andrea Alzetta, an insurgent agitator from a movement that squats in empty properties – known as “Tarzan” in Italian revolutionary circles.

In an exchange of letters that could only belong to the transformed papacy of Jorge Mario Bergoglio, Alzetta addresses the pontiff as “my dearest Pope Francis”. His holiness replies with a pledge of “warm encouragement” for the latter’s occupation of scenic buildings and grounds right next door to his papal summer residence

Their exchange comes as Francis is trying to stave off a backlash from the church’s conservatives over homosexuality and divorce. “Incredible!” Alzetta said. “I’d never in my life have thought I’d write to the pope, and that he’d reply! However, nowadays who are we supposed to address ourselves to?”

The unexpected correspondence has its origins in an occupation in May of two buildings called La tenuta Vaselli, set in beautiful gardens with a view of the lake and hills of Frascati, a kilometre from the papal residence at Castel Gandolfo.

The choice of location was no coincidence: Alzetta’s group, Action Diritti in Movimento (Action Rights on the Move), chose the site, he says, as a statement and contribution before the calendar of holy events starting on 8 December, called the Jubilee of Mercy and entwining the Vatican with the city of Rome.

Scores of occupiers were spearheaded by Action which has for years formed the kernel of Rome’s hardline squatting movement: they entered the grounds and stucco houses, apparently at the invitation of the current owner of the house, a descendant of the Vaselli family, to establish what Alzetta calls “a multicultural centre for welcome reception” of homeless people and migrants. “A model for the city”, he said. They remain there still – among the cypresses and pines in what Tarzan hailed down a loudspeaker, as the crowds moved in, as “the most beautiful place in the world, surrounded by the rich, noble and powerful”.

Among those noble and powerful neighbours was the Pope, and Tarzan – a former autonomist, member of the Communist Refoundation party and now city councillor with a new movement called Left Ecology Liberty – elected to try and get him on side. The squatters befriended nuns stationed at Castel Gandolfo, one of whom, Sister Damiana Esposto, offered to act as courier of a missive. The Italian language is famous for its elegant, often stilted, formality when addressing people in a letter, but Tarzan discards ostentatious etiquette, beginning, on letter-headed paper featuring a red star and bold black arrow: “Carissimo Papa Francesco ...”

In his letter, Alzetta writes how grateful the squatters are “for your dedication of a little time to listen to us”, and for the chance to “inform you of the conditions of several hundred families in emergency accommodation, whom we represent”. He refers to the “mafia capital” scandal in which crime syndicates exploited immigrants and homeless families, and appeals to “your sensibility” regarding the struggle of “the homeless, migrants and unemployed of the city … in hope of your kind reply”.

Somewhat amazingly, Alzetta got a reply – on paper headed Segreteria di Stato, Dal Vaticano, addressed to Sister Esposto and signed by Monsignor Peter B Wells, assessor for general affairs, on the pope’s behalf. Acknowledging receipt of the letter, Wells says “His holiness the pontiff takes to heart that of which he has been made aware, and sends word of paternal understanding and firm encouragement, and assures that … in his prayers he imparts from his heart an apostolic benediction” for Tarzan’s cause.

The pope will “never cease to promote the values of justice and solidarity … with organs which champion the weakest sectors of society”, Pope Francis ends by sending the comrades his “deep esteem”. The occupation stands, now blessed; homeless Romans and migrants have done up the empty rooms and call them home; boys play table tennis under the umbrella pines. “This pope,” says Alzetta, “is one of the few who stands without hesitation on the side of the ‘last’, who’s raised the matter of homeless migrants; who understands the importance of a welcome reception.

“True, part of the church is still connected to power, money and business, and I want nothing to do with that. But this pope stands with ‘the Last’. And now we ‘communists’ will work with priests and parishioners. We’ll be sending the children of the homeless to play football with priests!”