Speaking of Celtic Gaul

And of course some of the choicest nuggets are tied up in a musty-smelling book. Initial copyright is 1944 and a reprint date of 1970. The author cites sources from the 19th century as vital scholarship. It is a trip. And I found it in the stacks at my university's library.

And it is enlightening. Whatmough suggests that in southern Gaul—Provincia to the Romans—had a linguistic situation that progressed something like this:

Ligurian (supposedly Indo-European language of some sort or another)
Celtic languages of the continental variety
Greek
Latin

Though the Greek part of the stream is, I'm sure, a trading language with few native speakers as a portion of the population. Though the Romans had a bigger military component, I'm sure they were also traders. And also a small portion of the population. But that doesn't explain the how of latinization. From p. 24:

In its main features the history of the latinization, this term being used in its strictest (i.e. linguistic) sense, is very similar in Gaul to what it had been in Italy. In both lands there are records of languages spoken before the spared of Latin, and some hints, but no actual records, of still others. Moreover we do not suppose that the ancestors of the people whose linguistic remains are the oldest known to us in either Gaul or Italy were dumb. What we have to ask is the question what languages, so far as we can now tell, were spoken in the several regions of Gaul, and its frontier-districts before the spread of Romance (that is Latin) or Germanic speech. This ultimate fate of the pre-Latin dialects of Gaul, as in Italy, was that at last they were abandoned, almost everywhere, in favor of other forms of speech, usually Latin. And if, as some hold, modern Greek is in Italy nowhere descended from the ancient Greek of Magna Graecia, a view mentioned here only for the sake of comparison and not because it is thought to be truer than the opposite theory, no more is Breton in France descended from the ancient Keltic dialect of Brittany, but (like Albanian in Italy) was introduced there from outside. But Basque, spoken in the arrondissements of Bayonne and Mauléon, is usually maintained to be descended from Iberian, spoken in the ancient Aquitania and presumably anterior to Keltic. 

So I suppose to really get to the heart of the matter, I'm going to have to learn about the latinization of Italy too. Vae mihi! I seem to have opened a can of worms. As for the origin of Greek spoken in Italy today, I have zero information to allow me an opinion. More about the latinization of Gaul, from p. 29:

There is, however, a great contrast between Narbonensis and the three Gauls, where latinization was affected much more slowly and was not in fact complete before the sixth century of our own era. The spared of Christianity had much to do with the introduction of Latin into the remoter parts of Gaul, and, outside of the towns and permanent camps, Christian preachers must have played at least as large a part as Roman soldiers, traders, and officials in spreading the Latin at the same time that they spread the faith of the Church. It is, therefore, all the more remarkable that a large proportion out of the total number of dialect inscriptions preserved to us in Gaul have been discovered in southern Gaul, which was earlier and more rapidly latinized, and not from Tres Galliae, which maintained their Keltic speech longer and more tenaciously, thoroughly latinized as the whole of Gaul was in the long run.

Well. That's a surprise. I wouldn't have expected that the church was the final nail in the coffin of Celtic Gaul, if for no other reason than the Romans had latinized the rest of the Celtic-speaking areas under their control. Interestingly though, it does help explain why Insular Celtic does survive. Want to make me guess? Here goes: The Romans didn't care too much what language you spoke at home as long as you spoke Latin where it mattered—in official capacities. The other curious bit is that there is a lack of Celtic-language inscriptions in the north. I've got no explanation.

Some questions
•When did Ligurian die out as a spoken language?
•When did Greek die out in Gaul?
•What was the proportion of Greek speakers in Provincia?
•When did continental Celtic die out in Gaul?
•Do we know the route of the spread of Latin?
•Why did Breton manage to reverse the trend of latinization?
•And why did Breton come from Britain instead of Gaul itself?

Bibliography
Whatmough, Joshua. (1970). The Dialects of Ancient Gaul: Prolegomena and records of the dialects. Cambridge, MA: Harvard University Press.