The Latin alphabet as used by the ancient Romans corresponds to the modern capital letters. More precisely, our capital letters corresponds to the alphabet used for inscriptions in stone or other hard materials.

The capital letter V was used for both the vowel u and for the consonant u (usually written "w" in English).

Many hundreds of years later when the alphabets that are the ancestors of the modern small Latin letters were developed for writing on parchment with a pen (i.e. goose feather), the small letter corresponding to the capital letter "V" was "u".

So, for some time, Latin was written using the pair capital "V" and small "u" for both the vowel and consonant "u".

However, in all Romance languages the consonant "u" (English "w") had changed its pronunciation to the fricative "v", so when writing modern languages there was a need to distinguish "u" and "v". That lead to the creation of the capital "U" and of the small "v", and "Vv" were assigned to the fricative, while "Uu" were assigned to the vowel.

As another detail of the "U" writing history, the letter "F" was used in Greek to write the consonant "u" (English "w").

However the Latin language had the fricative "f", which did not exist in Greek, and there was a need to have a letter for it. The Romans chose "F" for the fricative "f", which forced them to reuse "V" (previously used only for vowel "u"), for both the vowel and consonant "u".

So, the modern Latin alphabet has five letters that were originally used to write some variant of "u": F, U, V, W and Y.

("w" was introduced in English because they still had the consonant "u", unlike the Romance languages, where "v" was assigned to the fricative sound; "Y", a different graphic form of "V", was introduced by the Romans to write Greek words, because the Greeks no longer pronounced the vowel "u" like the Romans, but they pronounced it like the German "u" Umlaut or the French "u").

thanks! very interesting.