 Complete the following phrase:  Many contemporary Italian regions already had different substrata before the conquest of Italy and the islands by the ancient Romans: Northern Italy had a Ligurian, a Venetic, and a Celtic substratum in the areas once known as Gallia Cisalpina Gallia on this side of the Alps; Central Italy had an Umbrian and Etruscan substratum; Southern Italy and Sicily had an Oscan and Italic-Greek substratum respectively; and finally, Sardinia had an 