After the Romans conquered the Gallo-Alpine tribes, the slow process of linguistic Romanization of the languages began. Ancient family and village names were either translated or an Italian suffix was added on to the end (ini, oni, ucci, etti, etc.). In this way, a translated Sicilian name could be the same as a translated Piedmontese name. Still, after the fall of Rome, language shifted back to the natives languages and dialects. What we had in 1860 were the hybrid languages of Roman-Latin and the various Cisalpine dialects. Had cultural and linguistic Romanization not taken place, the Italian peninsula would be just like the Balkans today in terms of constituting entirely different languages and cultures.
If you look at the "linguistic map of Italy," and then look at the nations of 1860 (or any map between the fall of Rome and the Risorgimento, or even the regions today), it always closely matches! There is always the "northern nations," the "Roman state," and the "southern nations." All separated by different languages with local dialects. As Americans, we have a hard time comprehending the way Europe was socio-geographically over the centuries. I could move to Montana, a thousand miles away, tomorrow and instantly become a Montanan. That's what we're used to. I could move From the Bay Area to Maine, and probably fit in better than I do here, even though I have no knowledge of the state. That would be like going from Ireland to Belarus. The cultural-geographical scale, up until very recently, was entirely different.
Within many Italian provinces, there exists even different native dialects (ex. Brescia). Sometimes there are even two different language families, and in parts of the Tri-Veneto area there are three different deep-rooted languages spoken (Italian, Venetian, and Ladin), and it was once four when the German-Cimbrian language was alive. [I would consider the South Tyrol to be a different dynamic since it was wrongly acquired after World War II.]
Gallo-Italic languages (Wikipedia)
The Gallo-Italian or Gallo-Italic languages constitute the majority of northern Italian languages. Among them are are Piedmontese, Lombard, Emiliano-Romagnolo and Ligurian, although there is some doubt about the position of the latter due to its retention of final /o/.
The Gallo-Italian languages have characteristics both of the Gallo-Romance languages to the northwest (including French and Occitan) and the Italo-Romance languages to the south (including standard Italian). Examples of the former are the loss of all final vowels other than -a; the occurrence of lenition; the development of original /kt/ to /jt/ (and often later to /tʃ/); and the development of front-rounded vowels (e.g. the change of /u/ to /y/). Examples of the latter are the use of vowel changes to indicate plurals, in place of /s/; the widespread occurrence of metaphony of stressed vowels, triggered by original final /i/; and the development in some areas of /tʃ/ instead of /ts/ as the result of palatalization of original /k/ before e and i. As a result, there is some debate over the proper grouping of the Gallo-Italian languages. Most commonly, they are grouped with the Gallo-Romance languages, but some Italian linguists prefer to group them with the Italo-Romance languages.
Traditionally spoken in Northern Italy, Southern Switzerland, San Marino and Monaco, most Gallo-Italian languages have given way in everyday use to Standardized Italian. The vast majority of current speakers are bilingual with Italian. These languages are still spoken by immigrants in countries with Italian immigrant communities. Ligurian is formalised in Monaco as Monegasque.
The Venetian language is usually considered to belong to a different dialect community, while some publications place it among the Gallo-Italian languages.