Latin itself dates certainly from the 6th century BCE, to which the oldest known Latin incriptions have been dated. At that point, it was the tongue of the people of Latium (now Lazio), the Italian region situated around Rome on the west coast of Italy. This early Latin was difficult reading to even the scholars of Classical Latin times, a comment made by several of them, with such things as a dative ending in -d.
At that time, four other related languages (with Latin, the Italic family of Indo-European) were spoken in other areas of Italy and Istria/Slovenia:
[ul][li]Faliscan, spoken only in Falerii (modern Civita Castellana) in northeast Lazio[/li][li]Umbrian, spoken in Umbria and the longest survivor other than Latin of the Italic tongues, lasting down to the first century BCE[/li][li]Oscan, covering all the peninsula south of Umbrian and Latin except the “heel”[/li][li]Venetian, spoken in a region equivalent to the Italian provinces of Veneto and Friuli-Venezia Giulia, the Istrian peninsula, and the western half of Slovenia.[/ul][/li]
By 100 BC Latin had expanded to eliminate all the above (except lingering rural enclaves of Umbrian), and thereafter spread with the Roman Empire across much of the Mediterranean littoral and western Europe.
The process by which Latin transformed itself into the Romance languages was a slow and nearly imperceptible one, more akin to the changes in English between Chaucer’s time and the present, where it takes seeing “chuse” in the U.S. Constitution or hearing “obey” and “tea” rhymed in Alexander Pope to remind us how things have changed in just a short time.