It seems to me that if both had accepted their areas of influence, and cooperated economically then they would have both gotten what they wanted. For Rome it was access to the silk road routes to India/China/etc, and for the Sassanids it would be Mediterranean Sea Port access across the entire ocean. Maybe their economies would have eventually been so entwined that war would be too costly. Also with that large border secure Rome could deal with the Germans, while Sassanids could counter the Hepthalites, and both could better handle the looming threat of northern Nomadic People's. So my question is are there any periods of time where trade between the two was at it's hight?