So how did the ancients pronounce the V? Or didn’t they pronounce the V sound at all? They certainly had both the U and the V sounds. Take, for example the Latin words via, vestis, vacare, vocare, and vulgare. The initial V sound is quite clear. But what about ultra, umbra, uti, and unctuarium. The V sound couldn't be used in these words. They have to be spoken with the U sound.
There must have been a quite simple spelling rule little Romans learned in school. When the letter V appears immediately before a consonant, it has the U sound. For example: Julius, magnus, and lumen. But when the V appears immediately before a vowel, it keeps the V sound: gravis, civis, and vivere.
Of course, a few exceptions existed. Remember the Romans borrowed many words from the Greeks and even borrowed from other lands they conquered. What I find fascinating is that we tend to do the same borrowing in English.
Almost every time we use a V, it's followed by a vowel; almost every time we use a U, it is followed by a consonant. Except, of course, when a word ends in U, in which case we almost always add a silent E: true, blue, glue, flue, et cetera. We do the same thing with the V: give, have, solve.
About the 15th century some scribes began the slow process of differentiate between the two letters. The two didn't finally part until the 18th century. But Did they finally part? Quite a few public buildings and monuments still use a v in place of a u and consider that expensive jewelry and watch company Bvlgari.