But Benedict also has set down his own demands.

The pope repeated calls for greater freedoms for religious minorities - including the tiny Christian community in Turkey - and denounced divisions between Christians as a "scandal."

Benedict has made reaching out to the world's more than 250 million Orthodox a centerpiece of his papacy and has set the difficult goal of "full unity" between the two ancient branches of Christianity, which split in the 11th century over disputes including papal authority.

"The divisions which exist among Christians are a scandal to the world," the pope said after joining Ecumenical Patriarch Bartholomew I to mark the feast day of St. Andrew, who preached across Asia Minor and who tradition says ordained the first bishop of Constantinople, now Istanbul.

The homage of the Orthodox feast day Liturgy also was highly significant to Roman Catholics. Andrew was the brother of St. Peter, who was martyred in Rome and is considered the first pope.

In a joint statement, the pope and patriarch stressed the need to "preserve Christian roots" in European culture while remaining "open to other religions and their cultural contributions."

The comments could send conflicting signals to Turkey after the Vatican suggested there was room in the EU for its first Muslim member. They could also serve as a rallying point for groups opposed to bringing a predominantly Muslim country into the bloc.

The pope also recalled how the faith was shaped by the encounters of early Christians with the scientific and intellectual traditions of ancient Greece. It was the same theological backdrop - faith and reason - that was the basis for his explosive remarks in September in which he quoted a medieval Christian emperor who described Muhammad's teachings as "evil and inhuman."

The pope avoided any direct mention of Islam after praying with Bartholomew at the St. George Church in Istanbul, capital of Christian Byzantium before falling to Muslim forces in 1453.

The echoes of the city's turbulent history were among Benedict's stops.

Haghia Sophia, once a spiritual center of Christianity, was converted to a mosque in the 15th century. The site became a museum following the secular reforms that formed modern Turkey in the 1920s.

The pope, wearing white robes, stopped often to gaze on Quranic passages carved in the ancient marble - in some places where crosses and the fish-shaped sign of early Christians were chiseled away. Above them were frescoes and mosaics that couldn't be touched by Muslims: figures such as Jesus and the Virgin Mary, who are regarded as revered predecessors of Muhammad.

Security for the pilgrimage has been stringent. But it grew even tighter as the pope moved about Istanbul. Police blockades virtually sealed off parts of the city's ancient heart. Snipers stood watch on the minarets added to Haghia Sophia following the Muslim conquest.

About 150 nationalists demonstrated against the pope's visit to the site, gathering at a square about a half mile away and urging the government to open the museum to Muslim worship. Nationalists viewed the visit as a sign of Christian claims to the site and a challenge to Turkish sovereignty.

"Haghia Sophia is Turkish and will remain Turkish," one protest sign read. Riot police surrounded the demonstrators to prevent them from reaching the site.

Of Turkey's 70 million people, some 65,000 are Armenian Orthodox Christians, 20,000 are Roman Catholic and 3,500 are Protestant. Some 23,000 are Jewish.

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