I disagree. Yes, Mesopotamia was usually controlled by the Parthians or Sassanids, but everywhere else was squarely Roman sphere of influence. And they never co

I disagree. Yes, Mesopotamia was usually controlled by the Parthians or Sassanids, but everywhere else was squarely Roman sphere of influence. And they never controlled Persia proper. That would be https://en.wikipedia.org/wiki/Safavid_Iran https://en.wikipedia.org/wiki/Safavid_Iran. See https://en.wikipedia.org/wiki/Gunpowder_empires https://en.wikipedia.org/wiki/Gunpowder_empires for a fairly stable rough division of geography both before and after they period too.