Pope Francis prayed on Saturday on the second day of his visit to Turkey alongside a senior Islamic cleric in Istanbul’s blue mosque.
The blue mosque, known officially as the Sultanahmet Mosque, opened in 1616 and is the most famous in Turkey.
Its popular name was a reference to the fine blue Iznik tiles in its main prayer room.
The Vatican City spokesperson described it as a gesture of inter-religious harmony and a joint “moment of silent adoration” of God.
Pope Francis took off his shoes as he entered the huge mosque before bowing his head in prayer for several minutes, facing Mecca and standing next to Istanbul’s Grand Mufti Rahmi Yaran.
A similar act by his predecessor Pope Benedict in 2006 drew criticism from conservative Catholics and some Muslims.
Halil Cil, 24, a hospital worker from Istanbul, said there was need to show respect for each other’s beliefs.
He said God willing the pope’s visit would help in this respect.
“We want to practice our religion in peace, as we want people to understand Islam,” he said. “More so we don’t want war. Islam is a religion of peace.
Hundreds of people, many of them tourists, watched from behind police barriers as the pope then walked to the nearby Aya Sofya museum, once the Christian church Hagia Sophia.
A group of school children waving Turkish and Vatican flags chanted “Long live Pope Francis” in Italian as the Muslim call to prayer rang out across the Sultanahmet square, the heart of Istanbul’s historic quarter.
Pope would later in the day, celebrate Mass at the Catholic Cathedral of the Holy Spirit and then meet the leader of the Orthodox Church, Bartholomew.
Discussions at Bartholomew are expected to focus on healing the schism in the Christian Church in 1054 that divided Rome and Constantinople.
Islamic State insurgents have captured swathes of neighbouring Syria and Iraq, persecuting and killing Shi’ite Muslims, Christians and others who do not share their ultra-radical brand of Sunni Islam.