The twenty-first letter of the English alphabet, which developed as the North Semitic waw was transformed to the Greek upsilon. The Etruscans, however, represented the "U" sound with the letter "V," as did the Romans. In Roman monument writing, the "V" was used interchangably with "U" but by the Middle Ages the two letters began to part company; "U" was used primarily in monument carving, while "V" was used in manuscripts. The two letters only took on their own unique identities after the Middle Ages.