Greeks and Russians often like to see the Roman Empire as Greek, since Greek was the lingua franca, and not Latin, at the time of Christ.
But that was only true in the east; the lingua franca of the west was always Latin, not Greek. But even in the east, Latin was the language of government and law (including the imperial court in Constantinople) until Justinian. Hence the Corpus Iuris Civilis was promulgated in Constantinople in Latin, not Greek. The Strategekon of the Emperor Maurice in the late 6th cent. also indicates that commands in the army were still given in Latin