Lisbon: Pope Benedict XVI begins a four-day trip to Portugal on Tuesday with an open-air mass before an expected 160,000 pilgrims amid lingering questions over the Vatican`s handling of paedophile priests.
Church bells are scheduled to ring out across the capital to mark the moment when the 83-year-old pontiff`s Alitalia plane touches down at Lisbon airport at 11:00 am (1000 GMT).
Benedict is likely to focus his message on the Church`s call to preserve Europe`s Christian roots and Portugal`s traditional family values during the visit, the centrepiece of which is to be a huge open-air mass in the shrine of Fatima on Thursday.
The pontiff will be welcomed to overwhelmingly Catholic Portugal by President Anibal Cavaco Silva days before he is due to sign into law a bill passed by parliament which would make Portugal the sixth country to allow same-sex marriage.
The pope is also likely to address the social problems facing one of Europe`s hardest hit economies.
"The pope will encourage institutions to lend a hand and show solidarity during difficult times," Carlos Azevedo, the auxiliary bishop of Lisbon and the visit`s co-ordinator, told reporters Monday.
"Europe needs to be awoken, there is a lack of strong values," he added. "If there was greater ethical conscience we would not have arrived at the current economic disaster."
The German pope on Sunday urged the faithful to "accompany him in this pilgrimage" and to pray "for the Church and especially for priests".
But he steered clear of any specific reference to the wave of scandals which have tainted the Church over allegations that the Vatican has for years covered up the sexual abuse of children by priests in various countries, including several in Europe and the United States.
The pope is thought by some Vatican observers to be most likely to address the issue of paedophilia in a speech to seminarians and priests in Fatima on Thursday.
Police predict around 100,000 people will line the 8.2-kilometre (five mile) route which Benedict will take by popemobile to the huge riverside Terreiro do Paco square, where he will celebrate the first of his visit`s three giant masses.
Earlier, he is to pray at the 16th century Jeronimos monastery, whose renowned religious carvings have made it a UNESCO World Heritage Site.
The "heart" of his visit according to the Vatican will be his stop in Fatima, the site where three shepherd children reported seeing visions of the Virgin Mary in 1917.
The pope`s visit to the sanctuary town comes exactly 10 years after his predecessor John Paul II beatified two of the children at the site, bringing them one step from sainthood.
The organisers say the open-air mass in Fatima on May 13 -- the anniversary of the first reported apparition -- is expected to draw between 300,000 to 500,000 pilgrims.
He will celebrate the final mass of his visit on Friday in Portugal`s second largest city Oporto.