Persian ( or ), also known by its endonym Farsi (English: ; Persian: ), is the predominant modern descendant of Old Persian, a southwestern Iranian language within the Indo-Iranian branch of the Indo-European languages. It is primarily spoken in Iran, Afghanistan (officially known as Dari since 1958 for political reasons), and Tajikistan (officially known as Tajiki since the Soviet era for political reasons), and some other regions which historically came under Persian influence. The Persian language is classified as a continuation of Middle Persian, the official religious and literary language of Sassanid Persia, itself a continuation of Old Persian, the language of the Achaemenid Persian Empire. Persian is a pluricentric language and its grammar is similar to that of many contemporary European languages. Persian is so-called due to its origin from the capital of the Achaemenid empire, Persis (Fars or Pars), hence the name Persian (Farsi or Parsi). A Persian-speaking person may be referred to as Persophone.