About one hundred years after Alexander the Great led the Greeks to the edge of the world known to the West, a powerful opposing force of Iranian people advanced from Asia. One of these was the Parthians, relatives of the Indo-European Scythians, whose homeland extended from the Aral Sea to the Caspian Sea. Around 247 BCE they conquered north-eastern Iran and advanced gradually to the west, until they captured the city of Seleucia on the Tigris in 141 BCE. Around 55 BCE King Orodes II reinforced the military camp of Ctesiphon, on the opposite bank of the river from Seleucia, thus forming the double city of Seleucia-Ctesiphon, the future see of the Church of the East. Since the Parthian expansion to the west occurred simultaneously with the Roman advance towards the east, a clash between the two ambitious powers was unavoidable. In 92 BCE they agreed to the Euphrates as a shared border. The Parthian initiation of diplomatic relations with Rome, as well as with China, helped foster trade along the Silk Road, which included a 1600-kilometre stretch through Parthia.Baumer, The Church of the East, p. 9
Photo by Wikimedia Commons.