Mithridates, an Arsacid who had become ruler of Parthia in 171, first expands Parthia's control eastward by defeating King Eucratides of the Greco-Bactrian Kingdom.

This gives Parthia control over Bactria's territory west of the Arius river, the regions of Margiana and Aria (including the city of Herat in 167 BCE).

"The satrapy Turiva and that of Aspionus were taken away from Eucratides by the Parthians."

(Strabo XI.11.2) These victories give Parthia control of the overland trade routes between east and west (the Silk Road and the Persian Royal Road).

This control of trade will become the foundation of Parthia's wealth and power and be jealously guarded by the Arsacids, who will attempt to maintain direct control over the lands through which the major trade routes passed.