Christians speaking Syriac (a form of Aramaic) trace their origins back to Saint Peter, who, according to tradition, established a church in Antioch in the first century. The apostle Thomas is said to have spread the Gospel to the Syriac cities of Edessa and Nisibis (now in Turkey). The Syriac Bible, known as the Peshitta, is based on the Hebrew Bible, which was translated into Syriac in the second century. The Gospel texts were codified in Syriac in the fifth century. The Syriac Church chose to follow the Miaphysite teaching of Saint Cyril, patriarch of Alexandria (r. 412–44), that Christ's humanity and divinity were combined in one nature, rather than the decision of the Council of Chalcedon (451) that Christ had two natures (human and divine). As a result, the Syriac Church became increasingly independent of the authority of the Church of Constantinople and Rome. In the same period, another Syriac-speaking Christian community developed farther east in the Sasanian Empire. Known as the Church of the East (once called the Nestorian Church), it was active far into the Arabian Peninsula.