Greek eventually replaced Latin as the main language of Byzantine administration. Although the Byzantine Empire inherited Roman institutions, most of its eastern population already spoke Greek or related Greek varieties, making Greek increasingly practical for government, law, religion, and education.
The transition was gradual rather than a single overnight switch. Latin remained important in imperial titles, military tradition, and legal texts for centuries. Justinian I’s sixth-century legislation was largely written in Latin, but later laws increasingly appeared in Greek. Under Emperor Heraclius in the seventh century, Greek became firmly established as the language of official administration.
This change did not mean every Byzantine subject spoke Greek. Armenian, Syriac, Coptic, and other languages remained important in different regions. Nor did the empire stop considering itself Roman: Byzantine citizens called themselves Romans, while Greek became the empire’s dominant working language. Over time, Byzantine Greek developed into Medieval Greek and eventually contributed to modern Greek.