who assumed the throne in 527, oversaw a period of recovery of former territories. Justinian, the son of an Illyrian peasant, may already have exerted effective control during the reign of his uncle, Justin I (518–527).^[26] In 532, attempting to secure his eastern frontier, Justinian signed a peace treaty with Khosrau I of Persia agreeing to pay a large annual tribute to the Sassanids.google In the same year, Justinian survived a revolt in Constantinople (the Nika riots) which ended with the death of (allegedly) thirty thousand rioters. This victory solidified Justinian's power.^[27] Pope Agapetus I was sent to Constantinople by the Ostrogothic king Theodahad, but failed in his mission to sign a peace with Justinian. However, he succeeded in having the Monophysite Patriarch Anthimus I of Constantinople denounced, despite Empress Theodora's support.
The western conquests began in 533, as Justinian sent his general Belisarius to reclaim the former province of Africa from the Vandals with an army of about 15,000 men. Success came with surprising ease, but it was not until 548 that the major local independent tribes were subdued.^[27] In Ostrogothic Italy, the deaths of Theodoric the Great, his nephew and heir Athalaric, and his daughter Amalasuntha had left her murderer Theodahad on the throne despite his weakened authority. In 535, a small Byzantine expedition sent to Sicily met with easy success, but the Goths soon stiffened their resistance, and victory did not come until 540, when Belisarius captured Ravenna, after successful sieges of Naples and Rome.^[28]

Byzantine expansion during Justinian's reign.

Nevertheless, the Ostrogoths were soon reunited under the command of Totila and captured Rome on 17 December 546; Belisarius was eventually recalled by Justinian in early 549.^[29] The arrival of the Armenian eunuch Narses in Italy (late 551) with an army of some 35,000 men marked another shift in Gothic fortunes. Totila was defeated and died at the Battle of Busta Gallorum. His successor, Teia, was likewise defeated at the Battle of Mons Lactarius (October 552). Despite continuing resistance from a few Goth garrisons and two subsequent invasions by the Franks and Alamanni, the war for the Italian peninsula was at an end.^[30] In 551, a noble of Visigothic Hispania, Athanagild, sought Justinian's help in a rebellion against the king, and the emperor dispatched a force under Liberius, who, although elderly, proved himself a successful military commander. The Byzantine empire held on to a small slice of the Spania coast until the reign of Heraclius.^[31]
In the east, Roman-Persian Wars continued until 561 when Justinian's and Khosrau's envoys agreed on a 50-year peace. By the mid-550s, Justinian had won victories in most theaters of operation, with the notable exception of the Balkans, which were subjected to repeated incursions from the Slavs. In 559, the Empire faced a great invasion of Kutrigurs and Sclaveni. Justinian called Belisarius out of retirement, but once the immediate danger was over, the emperor took charge himself. The news that Justinian was reinforcing his Danube fleet made the Kutrigurs anxious, and they agreed to a treaty which gave them a subsidy and safe passage back across the river.^[27]
Justinian became universally famous because of his legislative work, remarkable for its sweeping character.^[32] In 529, a ten-man commission chaired by John the Cappadocian revised the ancient Roman legal code, creating the new Corpus Juris Civilis, a collection of laws that came to be referred to as "Justinian's Code".
During the sixth century, the traditional Greco-Roman culture was still influential in the Eastern empire with prominent representatives such as the natural philosopher John Philoponus. Nevertheless, the Christian philosophy and culture were in the ascendant and began to dominate the older culture. Hymns written by Romanos the Melodist marked the development of the Divine Liturgy, while architects and builders worked to complete the new Church of the Holy Wisdom, Hagia Sophia, designed to replace an older church destroyed in the course of the Nika revolt. Hagia Sophia stands today as one of the major monuments of architectural history.^[21] During the sixth and seventh centuries, the Empire was struck by a series of epidemics, which would greatly devastate the population, contributing to a significant economic decline and weakening of the Empire.^[33] Thus, some historians trace to the period between Justinian's death and the accession of Heraclius the transformation of Classical civilization into Eastern Orthodox civilization.
After Justinian died in 565, his successor, Justin II refused to pay the large tribute to the Persians. Meanwhile, the Germanic Lombards invaded Italy; by the end of the century only a third of Italy was in Byzantine hands. Justin's successor, Tiberius II, choosing between his enemies, awarded subsidies to the Avars while taking military action against the Persians. Though Tiberius' general, Maurice, led an effective campaign on the eastern frontier, subsidies failed to restrain the Avars. They captured the Balkan fortress of Sirmium in 582, while the Slavs began to make inroads across the Danube. Maurice, who meanwhile succeeded Tiberius, intervened in a Persian civil war, placed the legitimate Khosrau II back on the throne and married his daughter to him. Maurice's treaty with his new brother-in-law brought a new status-quo to the east territorially, enlarged to an extent never before achieved by the empire in its six century history, and much cheaper to defend during this new perpetual peace – millions of solidi were saved by the remission of tribute to the Persians alone. After his victory on the eastern frontier, Maurice was free to focus on the Balkans, and by 602 after a series of successful campaigns he had pushed the Avars and Slavs back across the Danube.^[21]