The name of Iran derives immediately from Middle Persian , Pahlavi 'yr'n, first attested in this form in the inscription that accompanies the investiture relief of Ardashir I at Naqsh-e Rustam. In this inscription, the king's Middle Persian appellation is ardašir šahan šah eran (lit. "Ardeshir, king of kings of Eran") corresponding to the passage ardašir šahan šah aryan (lit. Ardashir, king of kings of Aryans) in the Parthian inscription accompanying the Middle Persian one. Though in English the name Persia was once the norm, Iran is today the preferred name.