The purpose of papal trips outside Italy is generally to rally the Catholic faithful and strengthen the local church's ties with Rome. Not so in this case. Benedict's priority in traveling to Turkey is to meet the Ecumenical Patriarch of the Eastern Orthodox Church, Bartholomew I, the spiritual leader of the world's 200 million Orthodox Christians. Both the pope and the patriarch are enthusiastic about healing the rift between Rome and the Eastern Orthodox Church, which split in 1054.

But whether the pope likes it or not, this trip has turned into a confrontation between Islam and Christianity. After enraging Muslims worldwide in September by quoting a medieval Byzantine emperor hostile to Islam, Benedict is now regarded with deep suspicion by many Turks. On the eve of his arrival, conservative Islamists staged mass protests in Istanbul with the slogan: "No to the pope!".

This visit could hardly have come at a more inconvenient time for Prime Minister Recep Tayyip Erdogan. Earlier this month, the European Parliament chastised Turkey for continuing to deny Cypriot vessels access to its ports and for dragging its heels on democratic reforms. Then Turkish nationalists booed Erdogan at the funeral of former premier Bulent Ecevit and accused him of wanting to turn Turkey into an Islamic state.

There's also pressure from another quarter. The pope has encouraged expectations among Eastern Orthodox Christians that he will raise the issue of religious freedom in Turkey. A senior Christian prelate in Anatolia has said that this trip will provide an opportunity for the pope to highlight "the plight of the churches in Turkey."

Ankara is prickly about suggestions that Christians in Turkey might be in any sort of "plight." Though Turkey's population is about 98 percent Muslim, it is a secular state which likes to view itself as a European democracy. Compared to countries like Iran or Saudi Arabia, it is genuinely liberal in its approach to religious minorities. But by western standards, freedom of religion in Turkey is seriously restricted.

The fate of Halki Seminary is a case in point. That's the college where Orthodox clergy were trained until Ankara shut it down in 1971. Since then, the number of Orthodox clergy in Turkey has dwindled. And in recent years, the Turkish government has been vigorously pursuing a policy of confiscating church property.

Halki has become a barometer of religious freedom. The EU is insisting that the seminary be reopened, even making it a condition for Turkey's entry into the Union. Ankara argues that it cannot allow Halki to operate without letting radical Islamists launch their own schools, which could destabilize the country. That argument may seem plausible, but it also corroborates the allegations of religious discrimination. Particularly since the Turkish state promotes and actually funds the training of Muslim clergy.

Pope Benedict faces a huge diplomatic challenge on this trip to Turkey -- partly of his own making. Unlike many of his predecessors, he is not a professional diplomat. He's a scholar. And scholars let loose in the world of politics are notoriously clumsy. All his life he has opposed what he calls "the tyranny of relativism." When asked if it wasn't arrogant to insist that Christianity is superior to all other religions, he once replied with disarming candor: "But what if it's true?" He may win respect in the west for his courage and honesty, but he's unlikely to win many friends in the Muslim world.

John Berwick is DW-TV's religious affairs correspondent (ncy)