The vocalization of modern printed Bibles is a tradition that has its origins in the standard Tiberian system of vocalization. This was developed by the Masoretes of Tiberias, whose school was active in the early Islamic period down to the 10th century ad. This system of vocalization is found in extant early manuscript codices of the Bible that were produced by the Tiberian Masoretic school, the best known being the Aleppo Codex, and it reflects the Tiberian biblical reading tradition. The standard Tiberian vocalization continued to be transmitted in manuscripts produced in later centuries after the cessation of the Tiberian Masoretic school. These include the so-called Codex Leningradensis (St. Petersburg National Library of Russia I Firkovitch B19a), which was copied in the 11th century, and forms the basis of modern academic editions such as BHS and BHQ. There is remarkable uniformity in standard Tiberian vocalization across the medieval manuscripts, with only a few minor variations, some of which can be correlated with known differences between individual Masoretes during the Masoretic period.