The Achaemenid Empire or Achaemenian Empire, also known as the First Persian Empire, was the ancient Iranian empire founded by Cyrus the Great of the Achaemenid dynasty in 550 BC. Based in modern-day Iran, it was the largest empire by that point in history, spanning a total of 5.5 million square kilometres. The empire spanned from the Balkans and Egypt in the west, West Asia as the base, the majority of Central Asia to the northeast, and the Indus Valley to the southeast.

Old Persian is one of two directly attested Old Iranian languages and is the ancestor of Middle Persian. Like other Old Iranian languages, it was known to its native speakers as ariya (Iranian). Old Persian is close to both Avestan and the language of the Rig Veda, the oldest form of the Sanskrit language. All three languages are highly inflected.