A hail of arrows fired backwards by mounted Parthian archers while pretending to flee (cf. Just. Epit. 41,2,7: “saepe etiam fugam simulant, ut incautiores adversum vulnera insequentes habeant” ("often, too, they pretend flight, that they may make their pursuers less careful of being wounded"). There are also depictions of the Parthian shot, for instance on Chinese reliefs from the Han period (206 BC to AD 220).
Bibliography
1 H. von Gall, Das Reiterkampfbild in der iranischen und iranisch beeinflußten Kunst parthischer und sas…