Emperor Justinian I ruled the Byzantine Empire from 527 to 565 AD. He is best known for his ambitious efforts to reconquer lost territories of the Western Roman Empire and for his significant legal reforms, which culminated in the creation of the Corpus Juris Civilis, or "Body of Civil Law." This legal code has influenced many modern legal systems. Justinian also oversaw a flourishing of art and architecture, most notably the construction of the magnificent Hagia Sophia in Constantinople. His reign marked a period of cultural and economic prosperity, as well as challenges, including the outbreak of the Plague of Justinian.