Around the year 886, Patriarch Photius of Constantinople compiled statements about the rights and privileges of the Patriarchal Office and the Imperial Office that ended up being published in the Epanogoge (Introduction to the Law) of Emperor Basil I the Macedonian (867-886), which eventually went into Byzantium’s Basilika . A section of that is cited below. It is interesting to glean how Photius weaves the concept of the symphonia of Church and State according to a visible hierarcy, culminating in the thrones of Constantinople, both the Emperor and the Patriarch. I would be curious to know if this was understood to be only with respect to the Eastern territories or if this is how Photius understood the universal oikuomene. That would certainly contradict the ancient canons (3/28 of Constantinople 381 and Chalcedon 28), for the canons prescribing the throne of Constantinople as First always specified “next after old Rome”. In other words, it was understood that the throne of Old Rome still judges the affairs of Constantinople, even if Constantinople judges all the affairs in the East. That is certainly how it was openly understood at the Council of Constantinople (861) in the presence of the Papal legates (c.f. Dvornik, Byzantium and the Roman Primacy, 101-123). What Photius says here also makes me wonder just how Alexei Khomyakov would have taken Photius over a cup of tea discussing the nature of ecclesiastical authority.
In any case, one point that struck me was how Photius, as magnified as he is by the Eastern Orthodox Church, is as farthest from the idea of Constantinople as holding a mere “primacy of honor” (primus inter pares) that one can possible be save for the Roman Catholic doctrine of the Papacy. And here by “honor” I mean a primacy that entails no binding power of governance, as held by the contemporary Patriarchate of Moscow. He clearly saw the see of Constantinople as the final court of appeal, akin to how Elder Rome understood her prerogatives in relation to the universal Church by the conferrence of plenary power to St. Peter by the Lord Jesus. Lastly, it would be interesting to see how the below relates to the situation in Ukraine today. When and if the supreme throne is unworthy of communion, as Moscow has judged, to what throne is this matter to be resolved at? Any Byzantologist who knows the history of the oikuomenical Church of the Roman Empire can tell you that what is missing today is the Emperor to convene a truly Ecumenical Council whose domain it is to adjudicate these matters. But without such an entity as this, Eastern Orthodox ecclesiology has become, at least in terms of hierarchical communion, built upon foundations which are either completely fossilized (and far too deep in the ground to dig up), or prone to dead ends. I don’t think even Orthodox can have the patience to speak about the divine institution of the Pan-Orthodox synod. Of course, it is not as if Rome has much to boast for, either. It is certainly interesting, the world we live in.
“The Patriarch alone should interpret the canons adopted by those men of old [Church Fathers] and the decrees institutude by the holy synods. The patriarch should take care of and decide whatever problems arise from what was done and arranged, in particular and in general, by the ancient fathers in ecumenical synods and in provincial synods… Since the constitution, analogous to man, consists of parts and members, the highest and most necessary parts are the emperor and the patriarch. For this reason, the peace and happiness of the subjects [citizens of the realm] in soul and body lie in the agreement and harmony of kingship and priesthood in all respects. The [episcopal] throne of Constantinople, honored with dominion [over others], was declared by synodical votes to rank as the first [by the First Council of Constantinople in 381]. Thus those divine laws that followed decreed that matters brought before the other thrones should be referred to that [of Constantinople] for adjudication and decision.” 
Meanwhile, the current Patriarch of Constantinople, Bartholomew, is quite open to re-uniting with Rome. Just today was published the Patriarchal Letter of the Ecumenical Patriarch to Pope Francis for the Throne Feat of Sts. Peter and Paul. In this letter, the Patriarch affirms that the Roman Catholic Church is a “sister Church” to Constantinople (something which Patriarch Kirill of Moscow already admitted to as well), that the Council of Crete (2016) is “Holy and Great”, and that there is forthcoming an official document on Primacy in 2022. Happy reading.
 The Basilika was a 6 Volume collection of Imperial Law drawn from the Corpis Juris Civilis – Oxford Dictionary of Byzantium, Vol. 1, (eds.) A.P. Kazhdan (Oxford University Press, 1991), 265 & 703.
 Deno John Geanakoplos, Byzantium: Church, Society, and Civilization See through Contemporary Eyes (Chicago: University of Chicago Press, 1984), 137; “Patriarch Photios on the Powers of the Patriarch,” in Geffert B., Theofanis G. Stavrou, Eastern Orthodox Christianity: The Essential Texts (New Haven: Yale University Press, 2016), 115.