From Alexander Schmemann, A History of the Orthodox Church

Byzantium can in no way be considered merely a completed and outlived chapter of Church history. Not only does it continue to live in the Orthodox Church, but in a sense still defines Orthodoxy itself, constituting its historical form.

Just as modern Catholicism crystallized in the Middle Ages and in the era of the Counter-Reformation, so — perhaps to an even greater extent — did Orthodoxy acquire its present form, its historic canon, in Byzantium.