Pope Benedict XVI on Sunday called on Catholics to "be courageous" in defence of the traditional family as he celebrated mass before hundreds of thousands of faithful at a Zagreb hippodrome.
"Dear families be courageous! Do not give in to that secularised mentality which proposes living together as a preparation, or even a substitute for marriage!" he said on his second day of a visit to Croatia.
Secularisation threatens the family, the 84-year-old pontiff warned. "We are called to oppose such a mentality!" he said.
"Unfortunately we are forced to acknowledge the spread of a secularisation which leads to the exclusion of God from life and the increasing disintegration of the family, especially in Europe," the pope said.
The head of the world's 1.1 billion Catholics called for legislation that "supports families in the task of giving birth to children and educating them."
"Alongside what the Church says, the testimony and commitment of the Christian family ... is very important," he said.
The German pope also asked believers to "affirm the inviolability of human life from conception until natural death, the singular and irreplaceable value of the family founded upon matrimony"
After kicking his off his visit on Saturday by highlighting Europe's Christian roots and Croatia's place in Europe, the German pope firmly focused Sunday on family values.
The Vatican said 400,000 pilgrims attended the mass celebrated in the same hippodrome used by his predecessor Pope John Paul II in 1994 while the Balkan wars were still raging.
The conservative Croatian Catholic Church exerts heavy influence over the staunchly Catholic country sometimes called "the little Poland of the south".
Still even here, as in other parts of Europe, the Church laments that young people ignore its teachings on family and sex.
"Freedom without commitment to the truth is made into an absolute. ... Love is reduced to sentimental emotion and to the gratification of instinctive impulses without a commitment to build lasting bonds of reciprocal belonging and without openness to life," the pope warned.
The homily was heard by pilgrims of all ages and from across Croatia, neighbouring Bosnia and other countries.
They carried flags and wore scarves in the Vatican's white and yellow colours. Some had already arrived at 3:00 for the mass, which started at around 10:00 am.
Marijan Kirin, 86, from the eastern town of Slavonski Brod, arrived Saturday night on a bus and braved heavy rains to see the pontiff.
"For me as a Christian this is an exceptional thing. The faith means everything to me. The more I pray the happier I am," said Kirin, dressed in blue and looking much younger than her age.
"The pope's visit will further strengthen our faith. He spreads light, love and hope in the world," she added.
"The pope's words are important for both Croatia and the whole world, but the world pays attention to material things rather than to spiritual issues," said Boro Istuk, who came from southern Bosnia with seven family members to see the pope.
The 51-year-old pensioner told AFP that he had also seen John Paul II during his three visits to Croatia.
Later on Sunday, Benedict XVI was to pray at the tomb of controversial Cardinal Alojzije Stepinac, whose "real humanism" he praised on the plane to Croatia.
Stepinac, who headed Croatia's Catholic Church during World War II, was put on the road to sainthood by John Paul II in 1998. He is an important figure for Croatian Catholics, many of whom would like to see him become a saint.
However the beatification caused controversy as critics claimed the cardinal did not stand up against the persecution of Serbs and Jews by the then pro-Nazi Ustasha regime.
After the war, communist Yugoslav authorities accused Stepinac of collaboration with the Ustasha government, which he denied, and sentenced him to 16 years in jail.
The pope was set to return to Rome late Sunday.