The Pope arrives in Istanbul tomorrow at the start of a four-day visit that is as delicate and controversial as any undertaken by a pontiff in recent decades. His ostensible purpose is to make a pilgrimage to sites of Christian significance and to meet the Ecumenical Patriarch of the Orthodox Church, Bartholomew, to discuss ways of bringing the world's one billion Roman Catholics and 250 million Orthodox Christians closer together. But the underlying aim is to repair the Vatican's fractured relations with Islam, which are more a result of overreaction than anything the Pope himself has said.

He will have a hard task. The Pope has become caught up in campaigns by Muslim extremists and Turkish nationalists alike. The Turkish Prime Minister and Foreign Minister have snubbed his visit, pleading the need to attend a Nato summit in Riga. More than 20,000 demonstrators marched through Istanbul at the weekend, denouncing the Pope as an enemy of Islam. Across the Muslim world, religious leaders have seized, absurdly, on his citation of a late Byzantine emperor's criticism of Islam to accuse the Vatican of encouraging a new crusade.

Most of the uproar has been instigated by Islamists determined to take offence and to use the incident to incite Muslims against the West. They have played on the growing paranoia within the Muslim world and the anger with Western policies in the Middle East, Iraq and Afghanistan to portray Pope Benedict XVI as a determined opponent — an ahistorical interpretation that overlooks, for example, that Saddam Hussein was a determined enemy of Islam. To his credit, the Pope has refused to engage in polemics. Turning a cheek, he has expressed regret that his remarks have caused offence, stepped up efforts to engage moderate Muslim leaders and underlined his respect for Islam.

To its credit, Turkey has rejected calls to cancel the visit. But it has been made doubly controversial by Benedict's opposition, voiced before becoming Pope, to Turkey's membership of the European Union, saying it did not belong there because of its religion and culture. He arrives as the tortuous accession talks have reached a crisis point and when public opinion is angered at what it sees as a stream of concessions by the Government in Ankara and legal changes demanded by EU negotiators. This has spurred a virulent nationalism that denounces all attempts to integrate with the West. On the EU issue, the Pope is mistaken, and should at least signal that he does not believe the two cultures are fundamentally incompatible.

The Pope has been made a scapegoat for much unfocused frustration. Although a determinedly secular state, Turkey was for 500 years the seat of the Caliphate, and is feeling the pressure of Islamic revivalism among its neighbours and within its own borders. This has made Benedict's meeting with Bartholomew equally controversial. The Ecumenical Patriarch is primus inter pares within the community of Orthodox churches, but in Turkey his position is precarious. Christians there number only a few thousand, and suffer increasing harassment, including prosecutions for attempted prosyletising and concocted charges against Muslim converts to Christianity. After a split of more than 1,000 years, any rapprochement with Orthodoxy will be testing. To achieve this against a background of rising Muslim suspicion will demand all Benedict's tact, adroitness and humility.