Hebrew was written without vowels. For centuries the consonantal skeleton of the biblical text was stable while its pronunciation, phrasing and chant were carried orally. Between roughly the seventh and tenth centuries, scribal scholars called the Masoretes built that oral knowledge into the written page, working in several centres but decisively at Tiberias on the Sea of Galilee. They could not touch the consonants, so everything they added went above, below and beside them: niqqud, the system of dots and strokes fixing the vowels; teamim, cantillation accents that mark stress, divide clauses and encode the melody for public chanting; and marginal and end-notes, the Masorah proper, recording letter counts, unusual spellings and every place where the written text and the text as read differ.
The ben Asher family of Tiberias produced the tradition that prevailed. Two manuscripts carry it. The Aleppo Codex, written in the tenth century with its consonants copied by Shlomo ben Buya'a and its pointing and notes added by Aaron ben Moses ben Asher, was regarded as the standard; Maimonides used it. Roughly a third of it, including almost all the Torah, was lost after the 1947 riots in Aleppo. The Leningrad Codex of 1008, copied in Cairo in the same tradition, is the oldest complete manuscript of the Hebrew Bible and is the base text of Biblia Hebraica Stuttgartensia and therefore of most modern scholarly editions and translations.
The result is a text transmitted with extraordinary control. The Masoretes counted letters precisely so that copying errors could not accumulate silently, and the apparatus they built is why a modern Hebrew Bible can print vowels, accents and variant readings on a consonantal text nobody was permitted to change.