 Mi-verbs were “regularised” (transformed to their -o counterparts, or replaced altogether) in the Koine era and the transformation was almost complete by Byzantine times, with some vestiges of the -mi conjugation surviving only in the Passive voice in Modern Greek.Mi-verbs are an extremely ancient feature of Proto-Indoeuropean grammar.Sanskrit verbs are exclusively -mi verbs, all Latin verbs except the forms "sum" and "inquam" are -o verbs, whereas Ancient Greek verbs can be either.