Justinian (or Flavius Petrus Sabbatius) was born in 482, in Tauresium (present-day Skopje). As a child, Justinian was brought by his uncle Justin to Constantinople, the capitol of the Eastern Roman-Byzantine Empire, where he was given an extensive education. When Justin was named emperor in 518, Justinian became one of his closest advisors and generals. On the death of Justin in 527, Justinian assumed the throne of the Byzantine Empire and proceeded to expand the boundaries of the empire, regaining all the former territory of the Roman Empire under Theodosius I, with the exception of Gaul and central and northern Spain. Justinian's most significant and lasting acheivements was the codification of Roman law in "Corpus Iuris Civilis." Beginning in 528 under the direction of Tribonian, Justinian had the contemporary Roman law system as well as Roman juridical writings compiled and systematized. This became the most important codification of Roman law and was a model for many other systems of law. Besides the "Institutions," a four part textbook with the force of law, and the "Codex Justiniani," containing the "Novels" (later additional laws), the "Corpus Iuris Civilis" finds its quintessential meaning primarily in the "Digesta" or "Pandects," a collection of fifty books by noteable Roman judicial scholars. Today this is the most important source of Roman law. Proof of Justinian's penchant for building can still be seen today, especially notable being the church Hagia Sophia in Istanbul (in between a mosque and now a museum in the formerly Christian Constantinople), which Justinian had built for the crowning of the Byzantine emperors. Justinian died in 565 in Constantinople.