The first distinction between the letters "u" and "v" is recorded in a Gothic script from 1386, where "v" preceded "u". By the mid-16th century, the "v" form was used to represent the consonant and "u" the vowel sound, giving us the modern letter V. U and V were not accepted as distinct letters until many years later.

Why did Romans use V instead of U?

I have noticed when inscribing, the Romans tended to make their letters rather rigid, perhaps due to it being easier to inscribe a straight line than a curved one, thus making the letter look rather like a 'V'. In cursive, however, the letters tend to look more curved, making the letter look more like a "U".

When did V stop being U?

It wasn't until printing standardized letter shapes in the 1600s that the letter U became regularly used. First, in the 1500s, Italian printers started distinguishing between the vowel U and the consonant V. However, the V continued to be used for the U sound at the beginning of words.