I had a difficult time placing these sites (even with the Tigris-Euphrates) in a larger world context (like, "how large is this area?", and "relative to all Roman area").
So, I made a graphic that may be mildly helpful. [1]
Based on a quick check, these best I could find was the fort at Circesium (known as the "farthest fortress" (φρούριον ἔσχατον) of the Romans), which apparently existed by 256 AD. [2] However, the Roman Empire was basically over by 256 AD, and was in the process of splitting into West-East (Crisis of the Third Century[3]) and had likely already formed the breakaway Palmyrene Empire [4] ruled over by Zenobia.
All locations have therefore been placed on a map of the Palmyrene Empire (circa 271 AD) relative to Palmyra, Jerusalem, Petra, Cyprus, and similar well known locations. Map was made using the last Figure image from [5], the Palmyrene Empire Map from [6] and a Distort to 3-pt Edessa, Nisibis, and Zenobia.
> However, the Roman Empire was basically over by 256 AD
Instability during the crisis of the third century was not the end of the Empire in the slightest; especially considering that the Palmyrene Empire lasted hardly more than a single decade before it was reconquered by the Romans who held on to it for centuries longer.
The comment is in reference to the generally held height of Ancient Rome being ~100 AD. Afterward, largely 2nd order downward. This Wikipedia gif illustrates. [1]
The crisis article and late antiquity articles note:
> The crisis resulted in such profound changes in the empire's institutions, society, economic life, and religion that it is increasingly seen by most historians as defining the transition between the historical periods of classical antiquity and late antiquity.
> Diocletian (Emp: 284 AD), who began the custom of splitting the Empire into Eastern and Western portions ruled by multiple emperors simultaneously.
The Roman Empire was effectively broken, and mostly just oscillated until the final West-East break. It was already "customarily" split in two by 284 AD.
I read somewhere that the Roman Empire has not ended. It just morphed into the Catholic Church and has had various emanations(Austro-Hungarian empire) since then. One of the reason Christianity was chosen as the main religion was that it emphasized "turning the cheek" and followers already believed in one power, so it was thought that it would be easier to rule the masses this way.
Tangently Related: The Holy Roman Empire of the German Nation was the biggest mislabeling of human history - neither Holy, nor Roman, nor an Empire, not a Nation and not really German.
Thank you for these resources! The map in particular is very illustrative, I was having a hard time forming a mental image of the area in question without one.
The red square region is an image artifact of the overlay process. If you check the paper linked, there's a legend in the original image, which was then copied over to the combined image. I also discuss the image combining process a bit in the same comment.
Both sets of data were taken by image filtering the lower half of [1] for grey-black colors [(forts)], deleting all remaining imagery, transposing the image onto [2] using Photoshop, and then using Edit->Transform->[Scale,Distort] to image fit to a 3-point fit of Edessa, Nisibis, and Zenobia.
So, I made a graphic that may be mildly helpful. [1]
Based on a quick check, these best I could find was the fort at Circesium (known as the "farthest fortress" (φρούριον ἔσχατον) of the Romans), which apparently existed by 256 AD. [2] However, the Roman Empire was basically over by 256 AD, and was in the process of splitting into West-East (Crisis of the Third Century[3]) and had likely already formed the breakaway Palmyrene Empire [4] ruled over by Zenobia.
All locations have therefore been placed on a map of the Palmyrene Empire (circa 271 AD) relative to Palmyra, Jerusalem, Petra, Cyprus, and similar well known locations. Map was made using the last Figure image from [5], the Palmyrene Empire Map from [6] and a Distort to 3-pt Edessa, Nisibis, and Zenobia.
[1] https://i.imgur.com/dMZiloA.png (map I made)
[2] https://en.wikipedia.org/wiki/Circesium
[3] https://en.wikipedia.org/wiki/Crisis_of_the_Third_Century
[4] https://en.wikipedia.org/wiki/Palmyrene_Empire
[5] https://www.cambridge.org/core/journals/antiquity/article/wa...
[6] https://upload.wikimedia.org/wikipedia/commons/f/f8/Empire_o...