No-one has ever seriously questioned the exclusively monophonic character of medieval Byzantine ecclesiastical chant. The introduction of the drone, or ison singing, so familiar in contemporary Greek, Arabic, Romanian and Bulgarian practice, is not documented before the sixteenth century, when modal obscurity, resulting from complex and ambiguous chromatic alterations which appeared probably after the assimilation of Ottoman and other Eastern musical traditions, required the application of a tonic, or home-note, to mark the underlying tonal course of the melody. Musicians in Constantinople and on Mount Athos were probably oblivious of the rise of polyphony in the West, particularly after the formal break between the two Churches in the eleventh century, which was preceded by a long period of increasing estrangement. And with the Latin occupation of a part of the Byzantine Empire between 1204 and 1261, there was a general distaste for and rejection of the culture of the ‘Franks’.