One could say that “u” is a lazily written “V”. This was before we had the concept of upper and lower case letters. The roman alphabet used for fancy writing is pretty much exactly as our upper case letters. This was written with a flat brush, but they also had a more cursive everyday alphabet which is quite hard for us to read. Eventually writing with pens made the alphabet evolve into uncial letters that look kind of Tolkienesque. To mark the beginning of a verse they used the old roman fancy letter to have something that stood out in the text, i.e. a versal. “V” is a versal, and “u” was the running text version, but it was considered the same letter. For example they would write “Vniuersum” where we write “Universum” now. Then some complicated things happened in history that necessitated different sounds and the pronounciation split into v, u, and w, over time.