 Stress had become a phonological property and could serve to distinguish forms that were otherwise homophones of identical phonological structure, as in Spanish "canto" 'I sing' vs. "cantó" 's/he sang'.After the Classical Latin vowel length distinctions were lost in favor of vowel quality, a new system of allophonic vowel quantity appeared sometime between the 4th and 5th centuries.Around then, stressed vowels in open syllables came to be pronounced long (but still keeping height contrasts), and all the rest became short.