Saying there were certain things to which the Church must just say "No", the pope said the family based on heterosexual marriage was "a unique institution in God`s plan". The 79-year-old pope received a tumultuous welcome in this coastal city, where he will spend little more than 24 hours to close an international gathering of Roman Catholic families. Tens of thousands of people cheering and waving yellow and white Vatican flags lined the route of the motorcade after he was welcomed to the country by King Juan Carlos at the airport. Pope Benedict first stop was at the site of a train crash that killed 42 people last Monday. Bowing his head in silence toward the pavement outside Jesus station, Benedict made the sign of the cross, laid a wreath of flowers and asked the Madonna to console the bereaved. Speaking to reporters on his plane from Rome, the pope was asked about the gay marriage law and other changes in Spanish society that have been challenged by the Roman Catholic Church. He said he wanted to stress the positive aspects of family life in Spain and elsewhere but added that there were some problems that could not be ignored.