(It's surrounded by labels for desert, but I can't make out the labels on the island itself.)

https://en.wikipedia.org/wiki/Samosata is the modern city of Samsat https://en.wikipedia.org/wiki/Rhesaina is Ressaina (see http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:19...) https://en.wikipedia.org/wiki/Zeugma,_Commagene Zeugma is near modern-day Gaziantep

The location of historic Tharrana is apparently not finally known. Harran, Turkey is one possibility mentioned at http://www.euratlas.net/cartogra/peutinger/10_mesopotamia/me....

Since all reference points are in Turkey or Syria, best guess is that the cirular lake with the island is Al Jaboul Lake, 36.024360"N, 37.610087"E. It used to be a tributary to the Euphrates but no source I could find states exactly when that changed.

Here's an alternate proposal: Raqqah. Check it out on the map:

https://goo.gl/maps/ubW2hp1Wh6N2

It obviously isn't in a lake, but it looks like the the tributary coming down from Harran goes both west and east of Raqqah, making it an island of sorts. The shape made by the this "island" is reasonably close to circular. Finally, per the map, it's southeast of Zuegma and south of Harran.

Obviously hypothesising wildly, but this map is just way too much fun.

Edit: seems to be somewhere within the Iraqi marshlands: http://www.indiana.edu/~nelc/events/documents/Jwaideh/jwaide... (back then at least).

I believe it's this.

Presumably also because there wasn't much there at the time that would've allowed them to collect taxes.

> Presumably also because there wasn't much there at the time that would've allowed them to collect taxes. The Romans liked to portray Germania as poor and inhospitable. Part of the reason for that could be cognitive dissonance for never having conquered it.

Half of Cesar's Gallic War seems to be more than half about grain logistics (huge efforts to start the campaigns jus a few weeks earlier) and ripeness of the local crops. And that is even while he was likely trying to downplay all the robbery.

Production beyond the Rhine simply was not great even in times of peace, before the middle ages. Rome ended up controlling most of the German territory through client states anyway, even sending troops for punitive raids and propping up this or that friendly ruler, so they knew the economic potential of those lands pretty well; they just renounced full invasion because it was not worth the risk. At a time when they were already hitting what we could call scaling limits in their ability to mobilise troops over long distances, there was little appetite for going further North, where clearly there were no riches waiting for them. A similar assessment was done for Scotland, and rightly so.

Allow me to apologize for my lack of precision, I never intend to imply that they deliberately avoided "invader-friendly" crops. Wheat just had not spread that far, due to climate (not yet sufficiently adapted by breeding?) and/or cultural reasons: nomadism (well, more effect than cause I guess) and the fact that large scale forest clearances are the type of project that can only happen in presence of big organizations that are stable enough to enable such long term investments. Many German settlements still carry the name of the medieval nobleman who commissioned the original clearance (names ending in -rode, -roda, -reuth and probably some more regional variations), which implies that before the clearance, there was only wilderness.

This went on for many generations, it's not a "last days before the ostrogoths" exception. Competing "emperor startups" in an empire representing pretty much the entire known civilized world, surrounded by mostly harmless outlaw wilderness. It must have felt as natural and "could the world even be not like this?" to the people populating that world as nation states, competing militarily, economically and in the Olympics seem natural to us.

An abbreviated version may be found in https://www.youtube.com/watch?v=eS5Asjvhx6I :)

https://en.wikipedia.org/wiki/Thule

"There is no land beyond us and even the sea is no safe refuge when we are threatened by the Roman fleet....We are the last people on earth, and the last to be free: our very remoteness in a land known only to rumour has protected us up till this day...."