Then, too, there were suddenly Slavic speaking immigrants living in Greece itself, and throughout Anatolia, and absolutely no one bothered to make a record of their arrival, or to even appear to be interested in the phenomenon.
This is startling considering the vast sums the Eastern Empire had previously been spending to keep these people out!!!!
Fortunately there were enough people left so they could write about Justinian's Plague, and that, by itself, is remarkable since it left North Africa virtually unpopulated, and continental Western Europe simply disappeared as a place where humans lived.
China didn't bother to do anything for the next 500 years, not even trade luxury goods and gold with the Eastern Empire. The Silk Road simply disappeared and wasn't mentioned again for centuries.
But, there were bright spots. Mecca and Medina were relatively big time in that period, as was Petra ~ although the people there were incredibly poor, they were alive, had enough to eat, and actually managed to continue running a major site of religious pilgrimmage. They were even literate.
Imagine their surprise when shortly after Mohammad's death they were able to conquer the next nearest Byzantine province in a couple of days ~ and then roll on over everything but the old core area almost without resistance.
I think the fact that the good old boys in Mecca were able to absorb almost the entirity of the remainder of world civilization in a decade to be one which gives us an idea of exactly how terrible the Dark Age had been. It was bad; real bad; horrible; so bad that people forgot to write about it, even in the Eastern Mediterranean.
Byzantium's core area is frequently pointed to as an exception, and true enough the old city encompassed a vast area which was fully protected by walls. It also had on hand sufficient food for a 7 year siege. Since the events which precipitated the Dark Ages were of shorter duration, the city was able to survive and reassert order, although not to the degree it had before the Dark Ages.
We can envision Orthodox monks staring over the walls into the wilderness beyond writing down their thoughts about how red the sunsets were, and lo, and behold, we have such ancient documents available. On the other hand, the Byzantines did not, themselves, bother to take expeditions to the nether regions to see what had happened to everybody else. They had to wait centuries until new civilizations arose and folks from Venice could bring in mounted French knights to finally loot their precious city.
Of course, you discount the lack of enthusiasm on the part of the monophysites for defending the territory of the 'melkite' Emperor.
Now which 70 years was that? Certainly not during the reign of Justinian or his immediate successors during which notable iconography graced newly completed churches in Ravenna. Ones just before the iconoclasts took up the wholesale destruction of religious art?
And I guess George of Pisidia, the best secular poet of the Christian Imperial period doesn't count for anything, nor the composition of some of the most moving devotional poetry ever written (to my mind in any religious tradition)--the Great Canon of St. Andrew of Crete.
And wouldn't you know, the silk trade between the Empire and China died out just when some Christian monks manged to smuggle silkworm eggs back to Constantinople, c. 553, beginning an industry which lasted until the Empire fell.
Ah, and the Slav penetration into the Empire can't have been due to lack of strategic vision by Justin II and Tiberius II or the spend-thrift 'butter before swords' policies of Tiberius II which so depleted the treasury that even when a tactical genius, Maurice I succeeded to the throne the tide couldn't be stemmed.
Must have been a "Dark Age" with a complete collapse of the old order and loss of learning.