As the Achaemenid Empire grew to become the largest of its time—stretching from the Balkans to India—Old Persian served as the prestigious "royal language par excellence," though Aramaic often handled day-to-day administration.
Until recently, it was believed Old Persian was used exclusively for royal monuments. However, the 2006 discovery of an administrative clay tablet in Persepolis proved it was also used for practical recording. The Writing System: Cuneiform old persian
Old Persian emerged from the dialect spoken in the region of Persis (modern-day Fars, Iran). As the Achaemenid Empire grew to become the