Hundreds of thousands of "pro-family" protesters have gathered in the Italian capital to protest against laws giving more rights to homosexual couples.
The event drew people from all over the country
The proposed law would allow all unmarried couples greater rights in areas such as inheritance, but stops short of legalising gay marriage.
Hundreds of activists attended a counter-demonstration supporting the law nearby, in Rome's Piazza Navona.
The divisive issue is causing problems for Prime Minister Romano Prodi.
Catholics and Communists from Mr Prodi's coalition attended both rallies, magnifying the same divides that brought down his government in February, says the BBC's Christian Fraser.
'Test of commitment'
People from around the country gathered amid a carnival-like atmosphere for Italy's first "Family Day" rally, at Rome's St John Lateran square.
Music, clowns and games kept children entertained, while older demonstrators listened to speeches by Catholic officials.
"Living together is not family," protester Anna Manara, 58, told Associated Press news agency.
"A commitment such as marriage cements the bond, while other models make it easier to be together and therefore end up making it less valuable."
Reports say between 500,000 and 1.5 million protesters turned out.
The demonstration had the backing of the Vatican and Italy's Catholic bishops, although neither was involved in organising the protest.
At the counter-demonstration across town, Italy's Minister of International Trade and European Affairs, Emma Bonino, condemned the Vatican's interference in domestic politics.
"The Pope is just stepping in politics every single day," she said.
"You are not in a position to open the news, any evening at all, without a speech from the Pope, be it on Turkey, be it on whatever."
Franco Grillini, president of Italy's main gay rights group, Arcigay, said the country was "scared of diversity".
Yet Mr Grillini said he welcomed the Family Day rally.
"It will be a big protest against us, and that is the best advertisement we could ever have."
About 500,000 unmarried Italian couples are without shared rights or benefits.
Hundreds rallied to support the bill in Rome's Piazza Navona
They miss out on social benefits, property or inheritance, a situation that is now at odds with many countries in Europe.
When Mr Prodi came to power last year he promised his supporters that the government would bring in new laws to protect cohabiting couples.
But with only a razor-thin majority in the Senate, Mr Prodi needs the full support of all sides of his coalition, our correspondent says.
Recent polls showed that most Catholics in Italy are in favour of changes to the legislation despite Church opposition.