Pope Francis stood for two minutes of silent prayer facing east in one of Turkey's most important mosques, a powerful vision of Christian-Muslim understanding at a time when neighboring countries are experiencing violent Islamic assault on Christians and religious minorities. His head bowed, eyes closed and hands clasped in front of him, Francis prayed alongside the Grand Mufti of Istanbul, Rahmi Yaran, in the 17th-century Sultan Ahmet mosque, shifting gears to religious concerns on the second day of his three-day visit to Turkey.