We all know that literacy rates among the human population never really grew until more modern eras — say, the 1700s and onward. It only really started to grow exponentially from the 1800s and onward, even though, by then, the printing press was an “old” invention. That’s because the aristocracy still ruled the peasants in most parts of the world. Although we spend much time devoted to teaching people about all the great, modern aspects of the Byzantine Empire, this was one area in which it failed to deliver anything that could be construed as modern practice.
The low literacy rates of the Byzantine Empire were compounded by the momentous strife that occurred in regions where it dominated the economy sphere. Libraries were important sanctuaries for the wealthy, but many were destroyed or burned down — especially in Constantinople during the Fourth Crusade, for example.
The author of Scholars of Byzantium wrote: “Although there is some evidence, principally from the lives of saints, that elementary education was widely available, the impression must remain that literacy was less widespread and the average level of culture less high than had been the case in the ancient world. It is hard to imagine, for instance, a Byzantine province producing evidence of readers with such diverse and learned interests as those provided by the finds of papyri from the country districts of Greco-Roman Egypt.”
What this boils down to is that even old world Roman plebeians, as uneducated as they likely were, probably had more of a basic understanding of reading and writing than the Byzantines.
Ultimately, though, these were enormous empires with enormous reach. They were inhabited by many different types of people who made up subsets of a larger community. They had their own distinct cultures even though Rome had its own. It’s one of the reasons the Roman Empire was so successful — each conquered people was allowed to “keep” the attributes that made them unique. So literacy was likely dependent on region, culture, etc.