Overview
The Seleucids inherited the largest share of Alexander’s empire and governed it without ever dressing it. Greek and Macedonian settlers wore Greek clothes in their own cities; the Iranian population of the plateau kept the trousered, sleeved dress it had worn under the Achaemenids. The two systems ran side by side for two centuries with remarkably little exchange, which is itself the point: this was a ruling class living among its subjects rather than merging with them.
Key garments and style
Greek dress meant the chiton, pinned or sewn at the shoulders, under the himation; for men the chlamys, a short cloak fastened at one shoulder, and the kausia, the flat Macedonian felt cap — not a brimmed sun hat, which is the petasos, with which it is often confused. Kings appear on their coins in the plain cloth diadem that marked a Hellenistic monarch.
Iranian dress was the opposite in construction: cut and sewn to fit, with trousers, a sleeved tunic and often the kandys, a sleeved coat worn hanging from the shoulders rather than put on. To Greek eyes trousers were the marker of the East, and they stayed that way. The excavated Greek city at Ai-Khanoum on the Oxus shows how complete the separation could be — a gymnasium, a theatre and Greek inscriptions, deep in Central Asia.
Transition
When the Parthians took the plateau, Iranian dress returned to the court that mattered. Trousers, the fitted coat and the belted tunic became the clothing of rulers again, and the line runs from there to the Sasanian court style without a Greek interruption.