VATICAN CITY – The Sistine Chapel Choir, whose boys and men sing for the pope at all his Masses, performed in some illustrious company Friday morning.

The Westminster Abbey Choir, the world-renowned chorus that last year performed at the wedding of Prince William and Kate Middleton, joined the Sistine singers at a special papal Mass on Friday in St. Peter’s Basilica.

The historic event was seen as a perfect symbol of Christian harmony after centuries of discord.

It was the first time in its 500-plus year history that the pope’s personal choir sang as a single chorus with another choir, let alone one from the breakaway Anglican church.

And this isn’t any ordinary chorus: The Westminster Abbey Choir represents some of the finest of the Anglican church’s liturgical music traditions.

As a result, the symbolism of the choirs from the two churches uniting into one is enormous, particularly given Pope Benedict XVI’s stated aim of trying to unite all Christians.

The Mass marks the feast of St. Peter and St. Paul and is the day in which newly appointed Catholic archbishops receive a woolen stole, known as the pallium, as a sign of their communion with the pope.

“It’s the big Mass for underlining our links to the Holy Father, and to ask at that occasion for a non-Catholic choir to take part is deeply significant,” said Monsignor Mark Langham, the Vatican official responsible for relations with Anglicans.

Anglicans split from Rome in 1534 after English King Henry VIII was refused a marriage annulment. A half-millennium later, the two churches remain divided on a host of issues, especially female bishops and openly gay priests.

The differences prompted the Vatican in 2009 to make it easier for Anglicans uneasy with the liberal bent of their church to convert, throwing another wrench in ecumenical dialogue.

Organizers of the historic performance tried to downplay the differences or at least acknowledge that while deep theological problems remain, culturally the two churches can come together.

“In diversity you can find points of unity,” said Monsignor Massimo Palombella, the choirmaster of the Sistine Chapel Choir.

The two choirs are vastly different in style and, to many ears, Westminster is simply better.

“It is a splendid choir,” said the Rev. Jerome Weber, a Roman Catholic priest who reviews sacred music for Fanfare, the respected classical music magazine. Known for its precision, attention to detail and tonality, the Westminster choir is recorded twice a year by Hyperion, the British classical music label.

The Sistine choir, on the other hand, is often loud with a “harsh, bombastic tone,” he said.

Colin Mawby, the English composer, recently wrote a glowing review of the Sistine choir’s May concert at the Roman Catholic Westminster Cathedral, saying the pope’s singers had unfairly suffered from a bad reputation when in fact they were “a superb and expressive group.”

How the two actually blended remains to be heard.

“I think it will be a challenge to sing with them,” acknowledged Hugh Rowlands, a 13-year-old Westminster chorister who performed on Friday, and a day earlier at a private concert with the Sistine singers for Vatican officials in the Sistine Chapel itself.

Rowlands spoke at a reception Tuesday for the Westminster crew at the American Academy in Rome.

It was a welcome break from the daily grind for the choristers, who from the age of seven or eight are selected to attend the prestigious London choir school, where they live away from their families and carry a full load of academics while performing eight services a week, plus touring and concerts.

“There are some times when you can get very tired and you just wish you could sleep until noon when you wake up from a concert,” said 12-year-old Benjamin MacLean. “But it is very fun and the experiences you get on tours like visiting the pope or meeting the president, it’s amazing.”

The 19 Westminster boys came to Rome along with 12 lay vicars, the adult men in the choir. They may well be overwhelmed by the 35 boys and 22 men in the Sistine choir.

James O’Donnell, the music director of the Westminster choir, said both sides wre prepared to make some adjustments for the performance, but the music chosen – Palestrina, the 16th century Roman composer who represents the best of Renaissance polyphony – is common to the repertoires of both.

Benedict himself was behind the decision to invite Westminster to Rome, so awed by the quality of the choirboys when they sang for him at Westminster Abbey during his September 2010 visit. He specifically asked that the choirs be united as one, rather than alternate during the performance as is commonly done, said the Very Rev. John Hall, dean of Westminster Abbey.

Palombella, the Sistine choirmaster, jumped at the chance, eager to open up his choir to outside influences and shed the Sistine’s reputation as a historical relic closed to innovation.

“These meetings are good for both Sistine and Westminster,” he said in an interview. “Because it makes us learn the precision and detail of the English choirs, and it makes the English learn the warmth and intensity that the Italian choir has.”