Arsaces was originally the chief of the Parni, a nomadic tribe living near the Caspian Sea. They were excellent horsemen and archers.
Around 247 BC, while the Seleucid Empire (a Greek state that ruled Persia) was weakened by wars, Arsaces attacked and captured the province of Parthia.
This victory marked the beginning of the Parthian Empire (Arsacid Empire). Although he fought many battles to defend his new kingdom, his successors eventually built a great empire that rivaled Rome.