Nisibis 252-298: Who controlled the city?

[Nathan Ross]

in the 298, Nisibis (and Mesopotamia), seems to be part of the conquest of Galerius' campaign. So, it seems that Nisibis at the time was not part of the Roman Empire... but when was it lost?

Sources are extremely scarce and very hazy for the eastern frontier during this entire period (as you've found!). It looks like you've already established whatever might be best guesses for the earlier period - Nisibis seems to have been passed back and forth, but was more generally under Roman control.

The victory of Carus in the AD280s would appear to have solidified Roman rule over the eastern front up to the Tigris. However, things changed with the accession of Narses in c.293: according to Lactantius (de mortibus 9.5) he assembled an army and invaded the Roman provinces, "emulating the example set by his grandfather".

How far he got in this invasion is unknown. Aurelius Victor (Caesars 39.22) writes that he "greatly vexed the east", while Ammianus, Orosius and Jerome just mention that he "made war upon the east".

Several writers mention Galerius's first campaign against the Persians in 296, which was probably intended to stem their advance but which led to defeat somewhere between Carrhae and Callinicum, and then his second attempt in 298 through Armenia.

Festus (breviarium 14.57) writes that "after peace had been made (in 298/99) Mesopotamia was restored (to us) and the boundary re-established beyond the Tigris." This suggests that Narses had indeed captured Mesopotamia - or parts of it - but after his defeat in Armenia he was obliged to give it up.

Where Nisibis fits into this is unclear, except that the tetrarchs met there in 299 during the treaty negotiations, and the treaty itself established it as the sole trading point between the empires. We might assume that Narses captured it at some point c.296, or alternatively that it held out with a Roman or pro-Roman garrison, perhaps under blockade, until Galerius relieved it. It does seem to have been a formidable fortress, as Shapur II discovered a few decades later.