Rome vs. Parthia, essay help?

[Robert Vermaat]

But the Romans obviously never took all of Persia (as far as I know). So was it just in the late empire that Rome was getting more beat up by them? Wasn't it emperor Julian that tried to take them on, but ended up getting himself killed in the process?
My Roman Hist teacher never seemed to disagree with me when I mentioned this topic to him...

First of all, never trust what history teachers seem to think. I've encountered too many of them (including those who wrote the schoolbooks) harboring the most crazy notions about history, Roman history included.

You're looking at it from a wrong angle: a Roman campaign could be very successful without conquering the Persian Empire in full. Even occupying the capital for a longer time was, in my opinion, never a strategic aim for the Romans. By far the most of the wars between Rome and the Parthians and Persians was about the control of
a) Armenia and
b) Northern Syria
By far the most conflicts were fought to that end, and the same of course goes for the Eastern opponents: they never tried to conquer the entire Roman Empire either. By looking at it this way, you could of course say that the Persians and Parthians against Rome generally failed as well. But of course that's wrong, too.

To judge whether a Roman campaign was successful, you need to look at each campaign: why did it start, what was gained or lost, what was the result. You'll find that in most cases, territorial loss or a political conflict was the reason. Most of the time, Armenia was the cause of the trouble, either the Romans attempting to gain political leverage, or losing it. I think Rome was more aggressive there, but the Sassanids were very protective in that area as well. Another reason could be a Roman ruler (emperor or local governor) trying to gain glory by achieving a victory in the East (emulating Alexander without planning a real lasting conquest). We see some of that with the Persians too, the Parthians were never bent on conquest that much. But where the Romans stood in front of the gates of the capitals of Parthia or Persia a good number of times, Rome was of course never attacked by the opposite side. Only Constantinople was once besieged by the Persians (in 626 AD) - but even then the enemy never even reached the walls, but stood on the opposite banks of the Bosporus, leaving the actual siege to the Avars.

Another thing to look at is how the conflicts ended. After a number of battles, usually the parties came to an agreement involving the loss of a number of cities, and/or the payment of a certain sum of gold. Looking at the region over the period of 7 centuries, we see that the borders swung back and forward, but hardly changed. Neither side achieved lasting victory. However, the Romans survived when the Sassanid Empire eventually crumbled under the attacks of Islam during the mid-7th century. Only when that happened did the Romans lose the Syrian territory which they had fought over for such a long time.

So in general, I would say that you could not possibly conclude that the Roman campaigns 'generally failed' in the East.