Crash Course Linguistics Phonetics 2 - Vowels Episode 9 | 11m 34s | CC In English, we have 5 (well, sometimes 6) vowel letters, but way more vowel sounds. That’s where the IPA can help us! We ...

During the fixed initial-stress period of Latin (sixth to fifth centuries BC), internal open syllable vowels were totally neutralised, usually raising to /i/ (*per.fa.ki.oː > perficiō 'I complete'), ...

The reason for that is simple: classical Latin (for which the Roman alphabet was designed) had about 20 consonant sounds and five vowel sounds.

Kanehiro Nishimura, Patterns of Vowel Reduction in Latin: Phonetics and Phonology, Historische Sprachforschung / Historical Linguistics, Bd. 123 (2010), pp. 217-257 ...