Source unknown, probably combination of Christian symbols circle and triangle. The inclusion in Glagolitic of the letters Ⰺ, Ⰹ and Ⰻ with the same phonetic value was probably intended to imitate Byzantine Greek orthography where both η(eta) and ι(iota) were pronounced as /i/; it is possible that in the oldest texts Ⰻ rendered the i that alternated with tense ь.
