This volume is a sequel to the work I published, several years ago, under the title, _Byzantine Constantinople: the Walls of the City, and adjoining Historical Sites_. In that work the city was viewed, mainly, as the citadel of the Roman Empire in the East, and the bulwark of civilization for more than a thousand years. But the city of Constantine was not only a mighty fortress. It was, moreover, the centre of a great religious community, which elaborated dogmas, fostered forms of piety, and controlled an ecclesiastical administration that have left a profound impression upon the thought and life of mankind