The history of Christianity is bound-up with the Roman Empire - indeed the fullness of Christianity probably depends on this Empire, in its lineal manifestations.
Christianity arose within the Empire, and retains a major centre in Rome; yet Rome fell.
Rome fell, however, after having been replaced as Imperial capital by Constantinople (the second Rome) where Christianity reached its apogee in a Christian-Roman-Greek synthesis.
The third Rome was Moscow, descendant of Constantinople.
The enemies of Christianity - who conquered the first, second and third Rome - were respectively heathens (i.e barbarians - or the relatively uncivilised), Muslims, and Communists (Leftists); these also being purposive enemies of The Good as conceptualised by Christianity although in different ways.
(Significantly, there remains an alliance, or at least unity of purpose in opposition to Christianity, between the conquerors of the three Romes.)
I get the sense that (on earth) there is meant to be Empire, and the Empire is meant to be consciously Roman (i.e. Rome-descended) and Christian.
What of the British Empire?
The mythical history of Britain in Anglo Saxon and Medieval times had us descended from Troy - that is pre-Roman.
Then we were part of the Roman Empire, then not. The loss of Empire was a massive psychological (as well as physical) trauma - one fruit of which was the Arthur legend.
Awareness of our membership of the greater Empire of Christendom, with its centre in Constantinople, seems to have been weak in Anglo Saxon Times. Yet the 'Celtic' Christianity which came from Ireland (St Patrick), Scotland and Northumbria was classically Eastern Orthodox in form: it was monastic in focus, and the holy islands Iona and Lindisfarne prefigured Mount Athos.
From a Christian perspective, in terms of sanctity, 'Celtic' (actually Orthodox) Christianity was the high point of history in the British Isles.
Spiritually, therefore, Britain was a part of the Byzantine Empire - and this may have been more explicit than commonly realized, since around ten percent of the population fled from the Rome-backed Norman invasion from whom several thousand made their way to Constantinople and set up an English colony that lasted some centuries.
The second wave of 'Roman'-style Catholicism came up from the South East (Kent; St Augustine of Canterbury) - the restoration of linkage to Rome is palpable; and was reinforced by the Norman kings.
However, by the time the British Empire got going, the Reformation had intervened, and the awareness of spiritual links to the Roman Empire had dissipated.
Indeed, it had been replaced by active hostility to Rome and the Holy Roman Empire since Britain had been in constant conflict with Spain, France, Central European powers. Constantinople was gone, there was no link with the Orthodox world.
Perhaps that was the major flaw in the British Empire - it 'should' have been a continuation of the Christian Roman Empire, but it was not - and the British state evolved further and further away from any genuine aspiration to a divinely-sanctioned Monarchy.
So here we are - The great Byzantine Empire now almost entirely a matter of history, its memory vilified; yet retaining its power to inspire. Our task being to live among its ever-crumbling ruins, loyal to the spiritual ideal.