Istanbul (AFP) - Pope Francis on Saturday heads to Istanbul for the second leg of his first trip to Turkey, in a richly-symbolic visit set to include a tour of a mosque and a meeting with the Orthodox ecumenical patriarch.Francis will touch on several aspects of the extraordinary heritage of Turkey's largest city, which as Constantinople was the capital of the Christian Byzantine world until the Muslim Ottoman conquest of 1453.He will begin his visit with a tour of Hagia Sophia, the great Byzantine church that was turned into a mosque after the conquest of Constantinople but then became a secular museum for all in modern day Turkey.His every gesture will be scrutinised later in the day when he visits the Sultan Ahmet mosque, known as the Blue Mosque, one of the greatest masterpieces of Ottoman architecture.When his predecessor Benedict XVI visited the mosque in 2006, he assumed the Muslim attitude of prayer and turned towards Mecca in what many saw as a stunning gesture of reconciliation.The Vatican later made clear he had not actually prayed in the mosque but was "in meditation". Pope Francis could make a similar gesture.Later in the day the leader of the world's Roman Catholics will celebrate holy mass at the Catholic Cathedral of the Holy Spirit in Istanbul.He will then hold an ecumenical prayer in the Orthodox Church of St. George and a private meeting with Patriarch Bartholomew I, the "first among equals" of the world's estimated 300 million Orthodox believers.Francis and Bartholomew -- who enjoy warm relations -- will seek to narrow the differences between the two Churches that date back to the great schism of 1054."We are eagerly awaiting the visit of our brother, Pope Francis," Bartholomew said ahead of the visit. "It will be yet another significant step in our positive relations as sister Churches."Turkey's own Christian community is tiny -- just 80,000 in a country of some 75 million Muslims -- but also extremely mixed, consisting of Armenians, Greek Orthodox, Franco-Levantines, Syriac Orthodox and Chaldeans.Of these only the small Franco-Levantine and Chaldean communities regard the pope as the head of their churches. - 'Rising Islamophobia' - The pope held talks with Turkish President Recep Tayyip Erdogan in Ankara on Friday, calling for dialogue between faiths to end the Islamist extremism plaguing the Middle East.The pope's visit is seen as a crucial test of his ability to build bridges between faiths amid the rampage by Islamic State (IS) jihadists in Iraq and Syria and concerns over the persecution of Christian minorities in the Middle East."Inter-religious and inter-cultural dialogue can make an important contribution... so that there will be an end to all forms of fundamentalism and terrorism," he said.Erdogan -- who welcomed Pope Francis as the first foreign dignitary to his controversial new presidential palace outside Ankara -- for his part issued a strong warning about rising Islamophobia in the world."Islamophobia is rising seriously and rapidly. We must work together against the threats weighing on our planet -- intolerance, racism and discrimination," said Erdogan.Some 7,000 police will reportedly be on hand to supervise the pope's two-day visit to Istanbul. Amid heavy security, he was not expected to show the close contact with crowds that have been such a feature of his past trips. Join the conversation about this story »