Central to Brown's novel is the suggestion that Jesus and Mary Magdalene had a child together, with the bloodline continuing to the present day -- an idea that's offensive to many in both churches.
Father Igor Vyzhanov, secretary of the Department of Inter-Christian Relations at the Moscow Patriarchate, explained to RFE/RL why both Orthodox Christians and Roman Catholics see the popularity of "The Da Vinci Code" as part of a growing and disturbing anti-Christian trend in Europe.
"This is a book that offends Christians, it offends their beliefs. All over the world, we are seeing propaganda for this work. How can this be explained? What is this? We and the Catholics have the same view of such things. Nobody has the right to offend belief. There is freedom, but not freedom to slander others," Vyzhanov said.
Metropolitan Kiril's meeting with the pope has fueled speculation that better relations between the Moscow Patriarchate and the Holy See could be on the horizon.
The Orthodox and Roman Catholic churches have been divided since the 11th century over papal authority and other theological issues.
But opposing the controversial film is just one area in which the churches are finding common ground.
Other topics of mutual concern include the increasing acceptance of homosexuality, the prevalence of premarital sex and abortion, and the widespread availability of pornography. After meeting Benedict, Kiril told journalists that Orthodox and Catholic believers need to work together "to preserve Christianity in Europe."
Opposition by both churches to secularism is nothing new. What is new, as Vyzhanov explains, is that Orthodox Christians see the staunchly conservative Benedict as a Vatican leader they can do business with.
"We have always had respect for him personally," Vyzhanov said. "He is a respected theologian throughout the whole Christian world. Even before he became pope, I know that many Orthodox in Russia read his book and felt very positively about it. The well-known conservatism of the current pope, his criticism of liberalism, made a big impression on many."
The Holy See has long said reconciliation with the Russian Orthodox Church is a high priority, but Vatican overtures during the papacy of Benedict's predecessor, Pope John Paul II, were spurned.
Most notably, the Orthodox Church repeatedly resisted the attempts of the late John Paul -- who like Benedict, was a doctrinal conservative -- to get approval for a trip to Moscow.
Many observers said the historic animosity between Russia and John Paul's native Poland hindered attempts to improve Vatican-Orthodox relations.
Russian Orthodox leaders have found it much easier to cooperate with the German Pope Benedict, says long-time Vatican watcher John Allen. "The fact that he is German has improved things given the traditional tensions between Russians and Poles. And I think that it is also true that both the Catholic Church and the Orthodox Church are looking at what they would perceive is a climate of runaway secularism in much of Europe. And [they] perceive that they have much more in common with each other than that which divides them."
But despite the new unity in battling European secularism, Allen and other analysts say it is unrealistic to expect the Catholic-Orthodox thaw to go too far.
Deep-seated suspicions of the Vatican still linger in influential quarters of the Orthodox Church clergy and among the faithful.
As Allen explains, these include a fear of papal dominance and a resentment of what many Russian Orthodox consider Catholic proselytizing in the former Soviet Union.
"In the subtext to all of that, I think, is a general kind of anti-Western fear that still animates much Orthodox conversation and Orthodox thinking," Allen says. "And until those problems are resolved, the deep structural problems are resolved, I think it is probably too early and too optimistic to think that there is going to be some significant breakthrough in the short in this relationship."
Geraldine Fagan, who works in Moscow for the Forum 18 religious-rights watchdog, agrees.
"I think it's partly an alliance of convenience,"Fagan said. "Both churches are realizing in their own spheres that they are becoming, there is a public perception, there is a danger that they are becoming marginal bodies."
And despite this alliance of convenience, Benedict may have as hard a time as his predecessor securing a trip to Moscow, Fagan and other analysts say. Even as Metropolitan Kiril lauded his Vatican meeting earlier this month, he added that discussions of a possible papal visit to Moscow were not on the agenda.
Russian President Vladimir Putin celebrating Orthodox Christmas (CTK, file photo)
RELIGION AND SOCIETY: On December 21, 2005, RFE/RL's Washington office hosted a panel discussion on issues related to religious freedom in the former Soviet Union. Panelists included CATHERINE COSMAN, a senior policy analyst for the U.S. Commission on International Religious Freedom; FELIX CORLEY, editor of the Forum 18 News Service; and JOHN KINAHAN, Forum 18 assistant editor.
Cosman argued in her presentation that the Russian Orthodox Church receives preferential treatment from the government. She also expressed concern about the estimated 50,000 skinheads active in Russia. Corley focused on Uzbekistan and Turkmenistan, arguing that many governments in the region "fear institutions they can't control." Kinahan's presentation concentrates on the Uzbek government's assertions that Islamist extremists were behind the May uprising in Andijon.
LISTENListen to the complete panel discussion (about 90 minutes):
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THE COMPLETE STORY: A thematic webpage devoted to issues of religious tolerance in RFE/RL's broadcast region and around the globe.