Old Miezan is a mostly dead language.
Old Miezan was the language used by the Miezans as well as the various peoples that they conquered. The Legions still use some commands in Old Miezan, and their banners are marked with Miezan numerals.
When the Miezans were defeated, their language as it was fell out of favor. However, the people who they had oppressed were used to using it to the point that a corrupted form called Lower Miezan became popular, and is currently the most common language in Calernia.