Why does the Rosetta Stone have 3 kinds of writing?

The famous Rosetta Stone is a black granite slab inscribed with three ancient texts — two Egyptian and one Greek. It ultimately helped researchers decipher ancient Egyptian hieroglyphics, whose meaning had eluded historians for centuries. But why did ancient scribes include three different kinds of writing, or scripts, on this iconic stone in the first place?

The reason the stone has a trio of scripts ultimately stems from the legacy of one of Alexander the Great's generals. The Greek text on the stone is linked with Egypt's Ptolemaic dynasty, founded by Ptolemy I Soter, a Greek-speaking Macedonian general of Alexander’s. Alexander conquered Egypt in 332 B.C., and Ptolomy I Soter seized control of the country nine years later following Alexander's death. (Cleopatra, who died in 30 B.C., was the last active ruler of the Ptolemaic line.)

The stone isn't associated with Ptolemy I Soter, but with his descendant Ptolemy V Epiphanes, whose priests had the inscribed message composed in three different scripts that each played important social roles during the Ptolemaic dynasty.

Related: How do we decipher Egyptian hieroglyphics and other ancient languages?

A French Military expedition that was part of Napoleon's invasion of Egypt unearthed the Rosetta Stone in 1799 during construction of a fort at the town of Rashīd, according to the British Museum in London. Rosetta is the French name for Rashid, according to Oxford University Press.

The stone isn't complete, however; it's a broken part of a larger slab. But even though it's missing a big chunk of the hieroglyphs from its long-lost top section, the stone has the same message carved into it in three different kinds of writing — ancient Greek; Egyptian hieroglyphs; and Egyptian demotic script —  a cursive script that Egyptians used between the seventh century B.C. and the fifth century A.D., according to Britannica.

Egyptian demotic script was used for "the contemporary language used in everyday speech as well as administrative documents," Foy Scalf, head of research archives and a research associate at the Oriental Institute of the University of Chicago, told Live Science. In contrast, "the graMMAr of the hieroglyphic section imitates Middle Egyptian," the phase of the Egyptian language associated with Egypt's Middle Kingdom period, which spanned from about 2044 B.C. to 1650 B.C., he explained. "By the Ptolemaic period, Middle Egyptian was often used for very formal inscriptions, as Egyptian scribes considered it a classical version of their language whose imitation added authority to the text."