Pope Francis this morning visited two of Istanbul's great cultural landmarks, the Hagia Sofia museum that was orignally a church, and the Sultan Ahmed Mosque, where he stood in silent reflection beside the Grand Mufti of Istanbul in a moment of shared worship.
Police initially outnumbered pilgrims along the barriers that closed off the plaza that links the two historic buildings as the Pope arrived, an hour after landing in Istanbul from the capital, Ankara.
Watch: Pope Francis arrives at the Blue Mosque
Accompanied by Grand Mufti Rahmi Yaran, Pope Francis climbed the steps to the seventeenth-century mosque, also known as the Blue Mosque, which dominates the Istanbul skyline and was today framed by police helicopters.
The mosque, built from 1609 to 1616 under Ahmed I, is popularly known as the Blue Mosque because blue tiles cover the walls of its interior.
Francis removed his shoes before entering the building, where he was shown around by the Grand Mufti, another mufti, and two imams.
Meanwhile outside Hagia Sofia, just a few hundred metres away, a select group of some 200 pilgrims, waving flags bearing both the Islamic Crescent flag and the Vatican flag, sang the Allelulia, and drummed.
Watch: Pope Francis arrives at Hagia Sofia
Back in the enormous hall of the mosque, with his eyes closed and head bowed, Francis recalled the actions of his predecessor Benedict XVI, who paused for prayer-like reflection on the same spot in 2006, drawing some controversy.
The two religious leaders shared "a moment of silent adoration", a "beautiful moment" of inter-religious dialogue, Vatican spokesman Fr Federico Lombardi explained afterwards.
After just 20 minutes in the mosque Francis was driven along the plaza to Hagia Sofia, where he paused briefly to bless the singing pilgrims before touring the sixth-century former Greek Orthodox patriarchal basilica that was converted into an imperial mosque in 1453 and is now a museum.
Outside, the Muslim call to prayer sounded across the city. But it ended as Francis left the building, the pilgrims outside singing the Gloria as Francis blessed them from the papal car.
This afternoon the Pope was due to attend a Papal Mass at the Catholic church of the Holy Spirit before meeting with the Ecumenical Patriarch, Bartholomew.
Video: Pope Francis arrives at the Blue Mosque
Video: Pope Francis arrives at Hagia Sofia, is welcomed by pilgrims