The Parni were a nomadic Scythian tribe located between the Caspian and Aral seas.
In 247 B.C. they invaded northern Iran and established the Parthian kingdom. They expanded their domination over all of Iran and Mesopotamia at the expense of the Seleucid empire. This brought them into conflict with Rome.
The superiority of the Parthian mounted bowmen led to a great victory at the battle of Carrhae (53 B.C.) over the Roman legions when the opposing general, Crassus, was killed. This victory halted further expansion eastwards of the Roman empire.
In A.D. 224, Ardashir, a local chieftain in southern Iran revolted against the Parthian rulers and established the Sassanian Empire.