Ankara and the Vatican breathed a joint sigh of relief today as Pope Benedict XVI arrived in Istanbul for the last leg of his four day trip after holding a mass at a Marian shrine on a hillside at Ephesus - the only open air event of the journey and the most dangerous for him.

The Pope honoured a priest murdered in Turkey, and offered encouragement to the hardpressed Catholic minority in Turkey, where a number of priests have been attacked.

Both Turkish and Vatican officials had privately conceded that the mass, at the House of the Virgin Mary - where the mother of Jesus is traditionally held to have died - was the point at which the Pope would be "most exposed to danger" from Islamic extremists. Police marksmen watched from the surrounding woodland, helicopters clattered overhead, and only Vatican-accredited journalists were allowed to join the tiny congregation.

Turkey remains on high alert for the Pope's stay in Istanbul on Thursday and Friday, when he is due to visit both the Blue Mosque and Aya Sofia (Haghia Sophia), once a mosque and cathedral but now a museum.

At the mass, attended by a few hundred, the Pope referred to Turkey's Christian community as "a small minority which faces many challenges and difficulties daily". He paid tribute to Father Andrea Santoro, an Italian priest murdered at the altar of his church in February.

But the Pope's overall tone was upbeat, with the Vatican determined to build on the positive mood created at the outset of the trip on Tuesday by papal concessions over both Europe and Islam. In a reversal of the stand he took as cardinal he said he "favoured" Turkey's bid for EU membership, and also called for Christian-Muslim reconciliation, noting that Muslims and Christians "worship the one God, though in different ways".

Resplendent in gold robes with a green embroidered mitre on a platform decorated with white and yellow flowers - the Vatican colours - he appealed to the Virgin Mary to grant peace in the Middle east and around the world, noting that she was venerated by Muslims as well. "Let us sing joyfully, even when we are tested by difficulties and dangers" he said.

The congregation - one of the smallest any Pope has ever addressed - did their best to make up for lack of numbers, shouting "Benedetto" and waving Vatican and Turkish flags. The Pope appeared to have a slight cold and coughed frequently.

Some of those at the mass were British expats from the nearby resort of Kusadasi. "We don't have any problems with our Muslim neighbours" said Nicole Richards, cradling her nine week old daughter Ioni. Susan Rees, who runs a restaurant with her husband in Kusadasi, and her friend Jane Moulding, told the Times they were "Church of England if anything - but we wanted to show our support for Christian and Muslim coexistence".

The theory that the Virgin Mary died at Ephesus, near Izmir, stems from the Acts of the Apostles, in which Jesus instructs St John as he is dying on the cross to treat Mary as his own mother. Tradition holds that St John spread the Gospel in Asia Minor, taking Mary with him. A rival claim however is made for a "tomb of Mary" in Jerusalem.

The Pope prayed inside the domed stone house, built in the seventh century over the ruins of a first century dwelling. Catholic scholars discovered the house, set by a spring in a dip in the hills and shaded by plane trees and pines, after it was seen in a vision by Sister Catherine Emmerich, a nineteenth century mystic beatified by John Paul II two years ago.

The early Christian community at Ephesus was used as a base by St Paul, and was later the site of the Third Ecumenical Council in AD 431, which gave Mary the title "Mother of God".

The Pope today held the first of several meetings with Bartholomew 1, the Ecumenical Orthodox Patriarch of Istanbul and spiritual leader of 250 million Orthodox Christians, pledging to work for "the full unity of Catholics and Orthodox". The two denominations have been split since an eleventh century schism.

The Patriarch will be looking to the Pope for backing over the Orthodox Church's complaints that the secular Turkish state denies it juridical and property rights and has closed its main seminary.

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