Sure, the ancient borders have been shaded within modern Italian provincial borders, and thus are rough or "rounded to the nearest modern border." But I've checked this with other maps, and found that it quite accurately depicts Italian borders on the dates it covers.
There are two takeaways, one which is directly related to genetics:
1. Metternich's oft-repeated slur that Italy is just a geographic expression is nonsense. There is a 2000+ year history of the peninsula being unified, and 1800 years of Italy even including the islands, like Sicily.
2. So who then has a claim on being more Italian? You often hear Northern Italians say they do.
Well, surely it is the provinces that have been known as Italy the longest, those which were romanized first. And those are, in order, the ones in teal, green, and magenta on the map.
(As the map notes but doesn't make clear: Caesar crossing the Rubicon was so significant because that was the border of Italy!)
If one mentally superimposes on this geopolitical map an actual demographic map showing Roman colonies...
...one can rather easily see that the current genetic clines of Italy are at least partly explained by which regions were first unified as Italian / Roman.
This brings me to what any college-level history student can tell you: for hundreds of years, Rome was an exporter of humans. Romans and Latins were wealthy compared to others in the world, and had lots of children, and their dominant political situation meant they could settle colonies at will.
It's time to consider that the genetic "southernness" of certain parts of Italy and the Mediterranean could easily be due to Roman colonies causing people there to resemble south-central Italians -- as opposed to the common yet misguided theory that more recent "invasions" to isolated Italian mountain towns by Saracens caused the people there to genetically resemble the latter.
