Why were the Romans unable to conquer the Persians in the same way as Alexander?

by Nadal12

It strikes me that the Romans start in a stronger position than Alexander when they first encounter the Persians and should theoretically have been able to carry out a similar invasion plan of replacing the Persian leader with the Emperor/Senate as Alexander did. The Persian Empire in Alexander's time also seems objectively larger and more powerful.Were they unwilling to do so or unable with their more Western ambitions taking up their resources?

Tiako

The Romans sacked Ctesiphon, the Parthian capital, four times, three during the Parthian period. However, the Romans already had a massive imperial state and were not terribly interested in adding new territory. Trajan had one of the very few attempts to actually conquer Mesopotamia (not Persia, however), but after sacking Ctesiphon the administration was bungled and the attempted Mesopotamian broke off.

By and large, during the first century where we have the best information neither the Romans or the Parthians were terribly concerned with aggressive action against either other, and their conflicts were largely over Armenia, as imperial rhetoric from both meant neither were willing to give the region up. Nero's clever solution was to allow the Parthians to choose a successor (as the Armenians themselves leaned towards Persia), who would then travel to Rome for coronation.

DonJimbo

My understanding from Plutarch is that Julius Caesar intended to campaign in Persia, but his assassination stopped that. Crassus (who was not a general of the same stature as Caesar or Alexander) did invade Persia, but that went terribly. Marc Antony also tried to invade, but also failed (although he survived). Augustus subsequently made peace with Persia in exchange for the return of Crassus's captured standards. The Empire was pretty much done with wholesale conquest at that point (except Britain, Dacia, and some parts of Germania). Much later, Trajan had success against Persia, but the gains were temporary. And late Rome was a basket case (crisis of the 3rd century, etc.).