Justinian I (c. 482 – 14 November 565) was Byzantine Emperor from 527 to 565. During his reign, Justinian sought to revive the Empire's greatness and reconquer the lost western half of the classical Roman Empire.

An aspect of his legacy was the uniform rewriting of Roman law, the Corpus Juris Civilis, which is still the basis of civil law in many modern states. His reign also marked a blossoming of Byzantine culture, and his building programme yielded such masterpieces as the church of Hagia Sophia, which was to be the centre of Eastern Orthodox Christianity for many centuries.

A devastating outbreak of bubonic plague in the early 540s marked the end of an age of splendor. The Empire entered a period of territorial decline not to be reversed until the ninth century.