SANTIAGO DE COMPOSTELA—Pope Benedict XVI warned Saturday of a return to 1930s-style "aggressive" anti-clericism in Spain and urged Europe to embrace God as he embarked on a two-day visit.

Benedict XVI set the tone for his visit even before he landed in Santiago de Compostela, Spain's holiest city, recalling an era when pro-Republicans killed priests and nuns and burned churches.

"Spain saw in the 1930s the birth of a strong and aggressive anti-clericism," the 83-year-old German-born pontiff told reporters aboard the papal plane.

"The clash between faith and modernity is happening again, and it is very strong today."

The comparison of the Spain of Socialist Prime Minister Jose Luis Rodriguez Zapatero with that of 1930s before and during the Civil War shocked the Spanish media.

"With all respect, your Holiness, someone has given you bad advice. Or better said, someone deceived you," said the online edition of the conservative El Mundo.

In Zapatero's Spain "churches are not burned and priests are not persecuted," it said. "On the contrary, the state collects funds for the Church and helps restore cathedrals.

In a homily at a giant open-air mass in Santiago's cobblestone medieval central square, the pope pleaded for Europe to open itself to God, lamenting as a tragedy a belief on the continent that God is an enemy of freedom.

"Europe must open itself to God, must come to meet Him without fear," he told 7,000 pilgrims who greeted him with cries of "Be-ne-dicto!" before he stepped onto a vast white stage, which had been dressed in a sweeping zigzag of purple flowers.

"Tragically, above all in nineteenth century Europe, the conviction grew that God is somehow man's antagonist and an enemy of his freedom," said the spiritual leader of more than one billion Roman Catholics.

Police spotters with binoculars scanned the crowd from atop the 18th-century building that is the seat of the regional government of Galicia on one side of the square.

The pontiff left later in the evening for Barcelona where he will sanctify Sunday Antoni Gaudi's unfinished masterpiece, the Sagrada Familia church, a symbol for the pontiff of the sacredness of family.

Benedict XVI is struggling to halt a retreat from the Catholic Church in Europe, where Spain is on the front line of social shifts allowing more access to abortion, fast-track divorce and gay marriage.

Santiago de Compostela, where a sprawling 12th century cathedral holds the purported remains of Saint James the Apostle, is a fitting venue to launch a revival of Christian values.

The eighth-century discovery of the remains of Saint James, later to be known as the Slayer of the Moors, became a symbol to rally Christian Spain, then pinned down by the Muslim Moors to the northern strip of the Iberian peninsula.

In the glittering crypt believed to hold Saint James' remains, the German pope knelt and prayed alone.

Dressed in a white cassock and a crimson cloak and stole, the pontiff then ascended to the central nave and embraced a painted statue of the first century saint clutching a staff.

The pope enjoyed an ecstatic welcome in the cobbled streets of Santiago de Compostela.

Thousands of pilgrims had lined the 11-kilometre (seven-mile) route from the airport as the papal cavalcade made its way to the centre of the city and its landmark cathedral, pausing at one point to allow the pope to lean forward from a window and kiss several babies carried to him by stewards.

Many cheered and waved flags or threw yellow and white confetti, the colors of the Vatican flag.

The Church was an all-powerful presence in the dictatorship of General Francisco Franco, who defeated the Republicans in the Civil War and died in 1975, but with democracy came an end to restrictions on politics, behavior and sexual mores.

Under Zapatero the country has gone much further, allowing gay marriage, speedier divorce and easier access to abortions, to the consternation of the Church.