How did the loss of Latin vowel length affect the development of Romance languages?

The loss of the system of contrasting vowel lengths was a fundamental phonological shift that occurred during the Vulgar Latin period, significantly altering the rhythm of the language.12

In Classical Latin, vowel length was a critical feature that distinguished meaning and governed prosody. As this system collapsed, long vowels generally became tense and short vowels became lax, introducing qualitative differences that replaced the earlier quantitative distinctions. This transition had several major impacts on the development of the Romance languages:32

• Diphthongization: Under the main stress accent, many vowels—particularly the "open" e and o—developed into diphthongs, a process often attributed to lengthening under heavy stress or the influence of following high vowels.4
• Syllable Structure: Even after the length system vanished, the distinction between "open" (light) and "closed" (heavy) syllables continued to influence how vowels evolved in different Romance dialects.3
• Vowel Weakening: The shift contributed to a broader restructuring of the language, where unaccented vowels weakened, sometimes disappearing entirely in certain positions, such as at the end of words.4

These changes, alongside a strengthening of the stress accent, were essential in the evolution from Latin into the diverse Romance languages spoken today.12