While the Empire encompassed various ethnic groups, Greek was the official language of administration, literature, and commerce. It evolved from the Koine Greek of the Hellenistic period, and it's the ancestor of modern Greek.
However, it's important to note that other languages were also spoken within the Empire's diverse population, such as:
* Latin: Used in some official contexts and by the Roman Catholic Church.
* Armenian: Spoken by a significant Armenian population.
* Syriac: Used by Christian communities in the East.
* Arabic: Spoken in areas under Arab rule or influence.
But Greek remained the dominant language and the one that defined the Byzantine cultural identity.