Pope Benedict arrived Saturday in the Spanish coastal city of Valencia to close an international meeting of Catholic families and comfort residents still mourning a train accident that killed 42 people earlier this week. As Sabina Castelfranco reports from Valencia, the pope emphasized the importance of family values.

Under a sweltering heat, cheering crowds were at the airport, waving flags and shouting out the pope's name, as his plane landed in the Mediterranean city of Valencia. The pope said the reason for this long-awaited visit is to take part in the Fifth World Meeting of Families.

In a speech, after his arrival in Spain, where the liberal government has legalized gay marriage, the pope said the family is a unique institution in God's plan, and the church cannot fail to proclaim and promote its fundamental importance.

"My desire," the pope said, "is to propose the central role for the church and society of the family, based on marriage."

Before his arrival, the pope told reporters on the plane that, according to human nature, it is man and woman who are made for each other, and give humanity a future.

Benedict was driven in a bulletproof pope mobile from the airport to the city center. Thousands lined the streets, and released yellow and white balloons - the colors of the Vatican - as he passed. His first stop was at the subway station where a train derailed this week, killing 42 people. There, he prayed for the victims.

At the airport, in a welcoming speech, the Spanish king said the presence of the pope "brings great relief to everyone, especially to families who have lost loved ones."

Pope Benedict visited the city's 13th century cathedral, where he handed the leader of the Spanish Episcopal Conference a letter addressed to the country's bishops. In the letter, the pope encouraged them in their activity at a time he said, of rapid secularization.

In the letter, he urged bishops to continue to proclaim that doing without God, acting as if he did not exist or relegating faith to the purely private sphere, undermines the truth about man and compromises the future of culture and society.

Pope Benedict also visited the Basilica of the Virgin of the Forlorn, the city's patron saint, then recited the Angelus prayer before thousands of pilgrims gathered in the square outside.

An evening gathering marks the closure of the World Meeting of Families.