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’), whereas in closed syllables /a/ was raised to /e/, but the other vowels remained distinct (*per.fak.tos>perfectus ‘completed’). Miller (1972) explains closed syllable resistance by positing internal secondary stress on closed syllables. However, evidence from vowel reduction and syncope suggest that internal syllables never bore stress in early archaic times. A typologically unusual alternative is proposed: contrary to the pattern normally found (Maddieson 1985), vowels had longer duration in closed syllables than in open syllables, as in Turkish and Finnish, thus permitting speakers to attain the targets for non-high vowels in closed syllables. This durational pattern is manifested not only in vowel reduction, but also in the quantitative changes seen in ‘classical’ and ‘inverse’ compensatory lengthenings, the development CVːCV > CVC and ‘superheavy’ degemination (VːCCV > VːCV).