In any case, for almost a thousand years the Patriarch of Constantinople presided over the church in the Eastern Roman (Byzantine) Empire and its missionary activity that brought the Christian faith in its Byzantine form to many peoples north of the imperial borders.
In history and in canonical literature (i.e. the Church's canons and traditional commentaries on them), the Ecumenical Patriarchate has been granted certain prerogatives (presbeia) which other autocephalous Orthodox churches do not have.