The wealth of the world flows through these lands: a fortune that could pay for any army that an ambitious king could imagine. The Parthians have the potential to be a great power – perhaps a great Empire – as they sit close to or astride the main trade routes from the east to the Mediterranean.
This is not something that endears the Seleucid Empire to the Parthian kings. The Seleucids have, from time to time, claimed to be the overlords of Parthia and, from time to time, have actually been strong enough to try and enforce their claim. Since that time the Parthians, under their Arsacid rulers (named after King Arsaces I), have fiercely maintained their independence. The Parthians are a nomadic people who conquered and settled in the area near the Caspian Sea in the 4th century BC as part of the Dahae confederation.