The parasang, also known as a farsakh (from Arabic), is a historical Iranian unit of walking distance, the length of which varied according to terrain and speed of travel. The European equivalent is the league. In modern terms the distance is about 3 or 3½ miles (4.8 or 5.6 km).
The parasang may have originally been some fraction of the distance an infantryman could march in some predefined period of time. Mid-5th-century BC Herodotus (v.53) speaks of an army traveling the equivalent of five parasangs per day.
In antiquity, the term was used throughout much of the Middle East, and the Old Iranian language from which it derives can no longer be determined (only two - of what must have been dozens - of Old Iranian languages are attested). There is no consensus with respect to its etymology or literal meaning. In addition to its appearance in various forms in later Iranian languages (e.g. Middle Persian frasang or Sogdian fasukh), the term also appears in Greek as parasangēs (Greek, Ancient (to 1453);: παρασάγγης), in Latin as Latin: parasanga, in Hebrew as parasa (Hebrew: פרסה), in Armenian as hrasakh (Armenian: հրասախ), in Georgian as parsakhi, in Syriac as parsḥā (Classical Syriac: ܦܪܣܚܐ), in Turkish as Turkish: [[Traditional Turkish units of measurement|fersah]], and in Arabic as farsakh (Arabic: فرسخ). The present-day New Persian word is also farsakh (Persian: فرسخ), and should not be confused with the present-day farsang (Persian: فرسنگ), which is a metric unit.