Nonetheless, like the German one the Persian border was an "eternal frontier" where no lasting headway could be made. Armies marched, cities and fortresses were captured and recaptured, and a lot of people died, but overall the balance didn't change.

Partly it was politics and ecology, but also because neither side had a distinct advantage that could not be overcome with superior generalship, stumped by sheer logistical limitations, or nullified by internal developements.