Tens of thousands of Catholics rallied in Madrid's Plaza de Colón Dec. 30 in support of the "traditional" family and against same-sex marriage and easier divorce.
Cardinal Antonio Cañizares conducted a Mass at the gathering and Pope Benedict XVI addressed the ralliers via video link.
Cañizares said the liberal policies of Prime Minister José María Rodríguez Zapatero threaten the very existence of society.
The pope said the family is “based on the unbreakable union of man and woman.”
Spain legalized same-sex marriage in 2005.
Organizers pegged the rally's turnout at 1.5 million.
“These atheist, irreligious governments want to make us believe that our life has no meaning,” one of the organizers, Kiko Argüello, told Reuters.
Spain holds a general election March 9. In recent polling, Zapatero's Socialist party held a 2 percent lead over the conservative Popular Party.
In response to the rally, Zapatero said his policies are supported by the “vast majority” of Spaniards and that the Roman Catholic Church should stop attempting to curtail citizens' constitutional rights.