Italian, the Successor of Latin

In the Roman Empire, spoken language (vulgar Latin) differed from written language (literary Latin).  Romance languages derive from vulgar Latin, the spoken variety.  The language that today we know as Italian is the one that has remained closest to the original Latin base, while other Romance languages have had external influences: French has been affected by Celtic and Germanic languages, Romanian by the Slavic languages, and Spanish by Arabic.
As the Roman armies expanded the extent of the Empire, Latin began to be used in general to administer it.  With the fall of the Roman Empire and the disappearance of Roman administration, the Latin language began to take on regional peculiarities in the many places it was still used.  In addition to this, the enormous distances separating one region from another, as well as the influence of other local languages combined to spawn the Romance languages.
The Romance languages that are most widely spoken in the world are Spanish, Portuguese, French, Italian, Romanian, Provencal, Catalan and Sardinian.
Currently, all the Romance languages use the Roman alphabet, although until the middle of the 19th century Romanian was written using the Cyrillic alphabet (used in Moldova until 1989); and during the Medieval period the Arab alphabet was used for certain Spanish dialects.