"Well the Roman Empire still existed. Justinian would have thought of himself as a Roman Emperor and most citizens would consider themselves Roman. Although he did bring Rome back into the Empire and reclaimed many lost provinces. Justinian made the Empire look like it once did, stretching from Syria to Spain. However, this came at such as cost that it left the Byzantines weak and over stretched. Here is how he did it: After Justian’s best General, Belasarius, defeated the Persians at Dara which secured peace in the East he was sent to invade the Vandal Kingdom in North Africa. The Vandal King Gelimur was decisively defeated at Ad Decium (meaning at the ten mile mark because it was ten miles from Carthage) then beaten again just outside Carthage. North Africa would stay under Byzantine rule the longest but during Justinian’s reign there would be several revolts due to insufficient pay. Next was the Ostrogothic Kingdom in Italy. Belasarius had just 7,500 men at first but thanks to his brilliance and some reinforcements he was able to conquer all of Italy up to the capital Ravenna. Then the Persians invaded the Byzantine Empire. Belasarius refused the peace offer and took Ravenna with by breaking a promise he had made with the garrison. The Persians were forced to withdraw and fighting stopped as the Plague of Justinian raged. ¼ of Constantinople’s population died and even Justinian got the plague but he survived. Afterwards, Italy would be retaken by barbarians and Belasarius went into retirement, although he would later be called to beat back some Bulgar raiders who got too close to the capital. This time Justinian sent 20,000 men under Narses who retook Italy and he even had men to spare to take Southern Spain. Justinian died with the Roman Empire restored to it’s former glory. However, after his death his successors were less capable and they lacked a brilliant general like Belasarius. After just a few decades Hispaspainia would fall and then Italy. In terms of territory this was the greatest extent the Byzantine reached and for 500 years they would be in decline." https://www.quora.com/Did-Justinian-revive-the-Roman-Empire-in-the-Byzantine-Empire-What-happened-after-his-death