What do you do, when you find that the mediaeval Greeks carelessly forgot to preserve a copy of some patristic text in which you are interested? Well, you have a couple of choices.
Firstly you can go and search manuscript libraries and see if you can find it. This option is rarely exercised, since dealing with many Greek libraries is only just preferable to torture.
Your other alternative is to see if anyone translated it into something else, before it was lost.
This happened a lot. Back in the 5th century, the Armenians sent off an expedition to Edessa, got a whole load of Syriac books, and translated these into Classical Armenian. They also set up a monastery in Jerusalem, which translated books and sent them back to the old country. As a result we have works by Irenaeus and Eusebius extant in no other language.
Old Slavonic is another language group that came into contact with the Greek world during the Dark Ages. The language was spoken by Old Slavs (of course). Once these had been taught literacy, they too acquired Greek literature.
I’ve found in Harnack’s Geschichte der altchristlichen Litteratur bis Eusebius, Theil I, halfte 2 — which I can’t find online — a list of ante-Nicene patristic authors whose works are extant in Old Slavonic. The list is more than a century old, but I think it would be interesting to look at, for those of us who know almost nothing about that language group. More in my next post!
Dark Ages? I don’t think so. In the Hellenistic era there is a major gap from 302 BC (where Diodorus ends) and 202 BC (where Polybius begins) for which we have no narrative histories. For all of the Byzantine era we have narrative histories, there is no such gap. Hence with the literal sense of a Dark Age it was most definitely not. The Byzantine Empire is not England where between the Romans leaving and the Viking invasions the place turned into a mess of fiedoms with noone care to record the events.
Now if the talk is of literary production it was not a dark age either. The low point in literary production is during the iconomachy yet that time is when very bright stars shine like St. John of Damascus. It is not proper to project the ideas and terminology of the West into other cultures, the Byzantine age was about as Dark as Tang China, it was the West that was in darkness.
There is a great academic debate whether Byzantium was middle ages, I am most definitely of the opinion it was not. The Empire was characterized by strong centralised imperial authority, quite the contrary from the weak power of the middle age kings of the West. Even the weakest emperors were much stronger than the king of France who had to go begging his knights just to get anything done.