Hundreds of thousands of protesters have taken to the streets of Paris over plans to give gay couples in France the right to marry and adopt children.
Three big marches converged on the Champs de Mars, a large park next to the Eiffel Tower.
France's Socialist government is planning to change the law this year.
But the demonstrators, backed by the Catholic Church and the right-wing opposition, argue it would undermine an essential building block of society.
The organisers put the number of marchers at 800,000, with demonstrators pouring into Paris by train and bus, carrying placards that read, "We don't want your law, Francois" and "Don't touch my civil code".
Police said the figure was closer to 340,000 and one government minister said the turnout was lower than the organisers had predicted. A similar march in November attracted around 100,000 people.
The "Demo for all" event was being led by a charismatic comedian known as Frigide Barjot, who tweeted that the "crowd is immense" and told French TV that gay marriage "makes no sense" because a child should be born to a man and woman.
'Test for president'
Although France allows civil unions between same-sex couples, Francois Hollande made a pledge to extend their rights part of his presidential campaign.
Centre-right UMP President Jean-Francois Cope said the rally would be a "test" for the president because there were "clearly millions of French people who are probably concerned by this reform".
The far-right National Front is also opposed to the change, although its leader Marine Le Pen stayed away from the march, arguing the issue was a diversion by politicians from France's real problems.
Despite the support of the Church and political right, the organisers are keen to stress their movement is non-political and non-religious, and in no way directed against homosexuals, BBC Paris correspondent Hugh Schofield reports.
An opinion poll of almost 1,000 people published by Le Nouvel Observateur newspaper at the weekend suggested that 56% supported gay marriage, while 50% disapproved of gay adoption.
The poll also said that 52% of those questioned disapproved of the Church's stand against the legislation.
Earlier polls had indicated stronger support for the legalisation of gay marriage.
As the marchers began arriving in the centre of Paris, four Ukrainian activists staged their own protest in St Peter's Square in the Vatican in support of gay rights.
The women from feminist group Femen appeared topless while Pope Benedict recited his traditional Angelus prayer.
Police moved to restrain the activists, one of whom was attacked by a worshipper brandishing an umbrella.