Trajan's invasion of Persia

Hello everyone. I am interested in Trajan's invasion of Persia, particularly its relation to the silk trade route. To what degree do you think that it was his motive to invade and was it a good idea? This is just a topic for fun. 

Parthia, not Persia, though the region is the same. His motive is discussed by Cassius Dio as being about glory and territorial expansion, although there's been some debate about economic motives that haven't really convinced everyone.

Now Dio was always a bit revisionist and critical of the Roman leaders - he refers to them as 'kings by another name' so bear that in mind when considering what he said about Trajan. Parthia had of course been a thorn in the side of Rome for a long time already and possibly Trajan was hoping to resolve the problem by conquest, as indeed he did with Dacia.

The Roman Empire was formed as a thalassocratic empire: it was basically formed as a network of city-states around the mediterranean sea under the hegemony of the city-state of Rome.

This empire expanded towards the northwest of Europe, as this region was very close to the Mediterranean region with direct access from the region of Gallia transalpina, where Julius Caesar based his invasion of Gaul.

Most Roman wars were not wars of conquest but instead wars for the security and hegemony of Rome. As noted by many authors, the empire of Rome was formed slowly in these defensive wars. Even Caesar's conquest of Gaul was defensive: he responded to the request for the defense of the southern gallic tribes around the region of Gallia Narbonensis (already a Roman province).

Trajan's invasion of Parthia was something very different. Not a defensive war; it was an attempt at invading the Parthian Empire, which was a Central Asian empire controlled by semi-nomadic horse archers. One should note that most of the border between Roman and Parthian territories was desertic, except for some small inhabitable areas around the Tigris river. Thus, it did not make any sense to annex territories there. This invasion also had no defensive purpose, as Syria was not under Parthian military threat for over a century: Trajan invaded it for the glory of doing so. Once he died, Hadrian took office, and he quickly abandoned Trajan's conquests.

I should also note that Trajan's Parthian campaign is not well documented in our sources.