From Middle Persian [script needed] (Stakhr, “strong(hold)”). According to Ernst Herzfeld, who based his conclusion on numismatic evidence, the Middle Persian word derives from Old Persian [script needed] (Pārsa-staxra, “"stronghold of Pars"”). The semantic change in New Persian is most probably due to the well known water reservoirs, dams and other irrigation apparatus built in the city of Istakhr by the Buyid prince 'Adud al-Dawla.