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
Hebrew alphabet Hebrew letters started being used to denote numbers in the late 2nd century BC, and performed this arithmetic function for about a thousand years. Nowadays alphanumeric notation is used only in specific contexts, e.g. denoting dates in the Hebrew calendar, denoting grades of school in Israel, other listings (e.g. שלב א׳, שלב ב׳ – "phase a, phase b"), commonly in Kabbalah (Jewish mysticism) in a practice known as gematria, and often in religious contexts. The numbers 500, 600, 700, 800 and 900 are commonly represented by the juxtapositions ק״ת, ר״ת, ש״ת, ת״ת, and ק״תת respectively. Adding a geresh ("׳") to