This is an impressive mosque, in a former church that has been identified as first St. Mary Diaconissa, then as St. Saviour Kataleptos and most recently as St. Mary Kyrotissa. It is cruciform, has deep barrel vaults and a dome with sixteen ribs. It originally had side aisles communicating with the nave, and galleries over the two narthexes. It is from the late 12th century, and has some of the old marble revetment. Strolling through Istanbul mentions it as the “most attractive Byzantine building in the city”. It also contained the frescoes of St. Francis of Assisi, now in the Archaeological Museum, the earliest cycle of frescoes of the saint’s life in the world.