The Rosetta stone is written in Greek and two versions of Egyptian. The reason is that the Egyptians were ruled by the Greek speaking Ptolemy dynasty so a major decree had to written in all three so that everyone in Egypt could read it. The actual text of the Rosetta stone describes the honors that the Egyptian priests were bestowing onto Ptolemy V and the tax breaks that Ptolemy was giving to the priest caste in return.

(The Great Courses – Alexander the Great and the Hellenistic Age)