Which vowel sounds were used in Classical Latin?

In Classical Latin, the vowel system was characterized by a distinction between long and short vowels, which was an essential feature of the language's prosody and verse. Because this system of vowel length was lost after the Classical period, the exact pronunciation is not known with certainty; however, it is assumed that long vowels were more tense and short vowels were more lax.12

The vowel sounds used in Classical Latin included:

• Long vowels: ā, ē, ī, ō, ū1
• Short vowels: ă, ĕ, ĭ, ŏ, ŭ1
• Front rounded vowel: Educated speakers also used a front rounded vowel (similar to the French u), which was borrowed from the Greek upsilon and used in words of Greek origin.1
• Diphthongs: The language utilized diphthongs such as ae (pronounced perhaps as an open ē in rustic speech), au (rustic open ō), and oe.1

Additionally, a neutral vowel was likely used in some unaccented syllables, and a long ē (derived from earlier ei) had likely merged with ī by the Classical period.1