About the Mystery of the Letters the mid-6th century, in which Mar Saba had played an important role. The anonymous author of the treatise declares he was prompted to the study of the secret meanings of the letters by the words of the Apocalypse, "I am the Alpha and Omega", and that he subsequently received a vision about them on Mount Sinai. The author proposes a re-modelled Greek alphabet reduced to 22 letters on the model of the 22 letters of Hebrew (discounting Xi Ξ and Psi Ψ), and with the Hebrew letter names. He then interprets these letters as symbolic figures of 22 works of
Biblical Hebrew source for the modern Hebrew alphabet. All of these scripts were lacking letters to represent all of the sounds of Biblical Hebrew, though these sounds are reflected in Greek and Latin transcriptions/translations of the time. These scripts originally only indicated consonants, but certain letters, known by the Latin term "matres lectionis", became increasingly used to mark vowels. In the Middle Ages, various systems of diacritics were developed to mark the vowels in Hebrew manuscripts; of these, only the Tiberian vocalization is still in wide use. Biblical Hebrew possessed a series of "emphatic" consonants whose precise articulation is disputed, likely ejective