The Romans had it out with the Parthians over and over again.
And the Parthians weren't even Mohammedan. This is classic East and West stuff. Civilization vs. the barbarians. And the barbarians eventually flooded the empire by immigration and higher birth numbers. It is kind of the same thing now only in the technological age things happen bigger and ever so much faster.
IIRC, weren't the Parthians stopping the spread of the Roman Empire eastward from the Levant (i.e. weren't the Parthians were fighting a defensive war as opposed to taking the battle to Rome proper)?