v

From Middle English lower case letter v (also written u), from Old English lower case u and respelling of Old English f between vowels and voiced consonants. * Old English lower case f from 7th century replacement by Latin lower case f of the Anglo-Saxon Futhorc letter ᚠ (f, “feoh”), derived from Etruscan letter 𐌅 (v). * Old English lower case u from 7th century replacement by Latin lower case v of the Anglo-Saxon Futhorc letter ᚢ (u, “ur”), derived from Raetic letter u. Before the 1700s, the pointed form v was written at the beginning of a word, while a rounded form u was used elsewhere, regardless of sound. So whereas valor and excuse appeared as in modern printing, have and upon were printed haue and vpon. Eventually, in the 1700s, to differentiate between the consonant and vowel sounds, the v form was used to represent the consonant, and u the vowel sound. v then preceded u in the alphabet, but the order has since reversed.

来源：wiktionary