Many people have been confused with the names of "Byzantine Empire and Eastern Roman Empire". For it is the same thing!
Actually, the Byzantine Empire was the eastern Greek-speaking part of the Roman Empire. Roma fell to the barbarians of King Odoacer Heruli in the year 476. That is to say 51 years previously to the foundation of the Eastern Roman Empire in what was known as Byzantium, an ancient Greek colony.
So today we speak of the Western Roman Empire, which fell into the hands of the barbarians, being Romulus Augustus the last Roman emperor, based in Rome.
On the other hand, the Eastern Roman territory had its capital at Constantinople, now Istanbul, Turkey. King Constantine (Roman) rebuilt the city of Byzantium and re-called it Constantinople on his behalf.
Then, from there on, Romans began to speak of the Byzantine Empire to the eastern part of the Roman Empire. The Eastern Roman Empire or Byzantine Empire lasted until 1453 when the Ottoman Turks took Constantinople and made it their capital in the name of Istanbul.
Justinian known as "The Great," was the emperor of the Byzantine Empire from 527 to 565; that is, he ruled for 38 years.
Justinian tried to recover all the territories of the Eastern Roman Empire and more. In Rome they spoke in Latin, but in Constantinople, Byzantine Greek was spoken.
Justinian was a prolific builder: The church of San Vitale in Ravenna with precious mosaics; the Hagia Sophia, which became the world's largest to date mosque. Byzantine art was generously supported by religious mosaics, sculptures, paintings, as well as architecture.