In inscriptions dating to the early Roman Empire, it is used frequently but inconsistently to transcribe the long vowel /iː/. In Gordon's 1957 study of inscriptions, it represented this vowel approximately 4% of the time in the 1st century CE, then 22.6% in the 2nd century, 11% in the 3rd, and not at all from the 4th century onward, reflecting a loss of phonemic vowel length by this time (one of the phonological changes from Classical Latin to Proto-Romance). In this role it is equivalent to the (also inconsistently-used) apex, which can appear on any long vowel: ⟨á é í ó v́⟩ /aː eː iː oː uː/. An example would be ⟨fIliI⟩, which is generally spelled fīliī today, using macrons rather than apices to indicate long vowels. On rare occasions, an apex could combine with long i to form ⟨Í⟩, e.g. ⟨dÍs·mánibus⟩.
The long i could also be used to indicate the semivowel [j], e.g. ⟨IVSTVS⟩ or ⟨CVIIVS⟩, the latter also ⟨CVIVS⟩, pronounced [ˈjʊstʊs, ˈkʊjːʊs]. It was also used to write a close allophone [i] of the short i phoneme, used before another vowel, as in ⟨CLAVDIO⟩, representing [ˈklau̯.di.oː].
Later on in the late Empire and afterwards, in some forms of New Roman cursive, as well as pre-Carolingian scripts of the Early Middle Ages such as Visigothic or Merovingian, it came to stand for the vowel ⟨i⟩ in word-initial position. For example, ⟨iNponunt in umeroſ⟩, which would be inpōnunt in umerōs in modern spelling.
The character exists in Unicode as U+A7FE latin epigraphic letter i longa, ⟨ꟾ⟩, having been suggested in a 2006 proposal.
Roman inscription, ca. AD 100, showing long i's contrasting with apices on other vowels, for example órnámentIs in line 3 (besides other words), representing the vowel /iː/.
Roman inscription, ca. AD 45, showing a use of the long i letter for the close [i] sound of Latin short ĭ before a vowel: claudIo.
Roman inscription, ca. AD 69, showing a rare use of long i with an apex in line 1, dÍs mánibus.
Manuscript samples in New Roman cursive from the 6th century. Top: quantum s(upra)s(cripto) emptori interfuerit. Bottom: tenentes igitur palestini.
Manuscript samples in Merovingian script from ca. AD 700. Top: et inponunt in umeros hominum. Bottom: in synagogis · et saluationis in foro.
- Gordon, A. E. (1957). Contributions to the Palaeography of Latin inscriptions. p. 216.
- Allen, Sydney (1978). Vox Latina: The Pronunciation of Classical Latin (2nd ed.). Gateshead, England: Athenaeum Press. pp. 37–39. ISBN 0-521-22049-1.
- Allen, Vox Latina, pp. 51-52, giving the examples dIes, prIvsqvam, pIvs
- Davud J. Perry (2006-08-01). "Proposal to Add Additional Ancient Roman Characters to UCS" (PDF). Retrieved 2018-09-30.