In 717 , a man from Syria came to the throne through a revolt , Leo III . He too was an excellent military leader whom soldiers trusted unquestionably . He and his son and successor , Constantine V , succeeded in stopping the Arab advance . The power of the provincial governors , over a hundred years after the introduction of the theme system , had reached an extent which was becoming dangerous for the central power , and Leo countered this by splitting the themes up into smaller units . He also strengthened imperial power over the Empire in other ways . He took money for his campaigns - among other things - from the Church . Leo was convinced that the portrayals of holy persons were idolatrous and utterly reprehensible . He therefore banned all figural imagery in religious art . This was in keeping with original Christian opinion and met with approval among many subjects . The majority , however , loved and revered the pictures and ascribed miraculous powers to them . A deep spilt resulted which lasted until into the 9th. century . Especially under Leo's son Constantine V iconophiles were banned and executed .

One of the 'side products' of iconoclasm was the crowning of Charlemagne as emperor already mentioned above . Irene , the wife of Leo IV , who had left a ten year-old son at his death , succeeded in securing her rule as regent . She reintroduced the cult of images against great resistance ; when her son took over rule , he withdrew this decision . On account of the scandal of his second marriage , Irene succeeded in having him deposed , had him blinded and ruled alone . But that allowed the Pope and the Frankish ruler the interpretation that the imperial throne was vacant , an interpretation which Constantinople naturally rejected . But Byzantium's position in Italy was completely undermined , so all that remained was the weak means of diplomatic protests . With the existence of two emperors , a part of the old world collapsed which had been based on the assumption of a universal empire .

The end of the iconoclastic controversy led to the first flowering of Byzantine art since Justinian I . Three hundred lean years were followed by three hundred fat ones . The loss of the south-eastern provinces , the militarisation of life through the themes and the permanent commitment of funds for defence expenditure had brought about an impoverishment of culture which was now surmounted . The adjustment had been successful and unleashed forces for creative processes . The mission in the Balkans and in Russia allowed the Orthodox Church , and with it Byzantine culture , to become the historically formative force there . The monk Cyril contributed particularly to this by developing the script named after him . It is used throughout the area of the Eastern Church , with the exception of the Greek areas .

It was once again a usurper who brought the Byzantine Empire to new brilliance . Basil I entered the service o Emperor Michael III as a groom and succeeded in rising to the top . He became co-regent , a common procedure in late Antiquity and the Middle Ages to secure succession , and had his predecessor murdered on 24-9-867 .

After this unkind act , he proved himself a excellent ruler . He began to tackle the overdue legal reform and had the legal codes , which until then had still been compiled in Latin , revised in Greek and adapted to the considerably changed social realities since Justinian . In the course of this , the division of tasks between Church and Emperor was fixed . The patriarch was responsible for the salvation of the subjects' souls , the ruler for their physical well-being . The Greek language became binding for court titles , the emperor was called 'Basileus' from then on , the Greek equivalent to the Latin 'Imperator ' .

Basil I laid the foundation for the military successes of his sons who led the Empire to its greatest expanse in the Middle Ages . In contrast to him , who had worked his way up from humble conditions , his children received an excellent education and were early initiated in the business of government .

Leo VI who , after the death of his father in 886 , continued his work , was given the epithet 'the Wise' already during his lifetime . Leo completed the legal reform and strengthened the position of the Emperor in the course of this . While a senate , as a vestige of Roman tradition , had still retained certain rights up to then , this institution was now abolished . Only the ruler could promulgate laws , even if he was himself still bound by those laws . The inner strength of the Empire permitted a restructuring of the themes which were made even smaller and deprived of their sub-units . Their leader was not so respected in rank as a commander of a unit of troops in the capital .

After Leo's death , the continuation of the dynasty was at risk . His son , Constantine VII , who had been born in a special purple red chamber in the palace , and thus received the epithet 'Porphyrogennetos' , was still too young . Leo's brother Alexander was luckless in his actions . After he too had died , the Bulgarian Tsar Simeon raised claims to the Byzantine throne and marched up to the walls of Constantinople with an army . Once again , the strategic position of the city proved a blessing ; both parties started negotiations during which the acceptance of the title of a Bulgarian Tsar and betrothal of Simeon's daughter to Constantine eased the tension . These concessions led to a palace revolt as a result of which the Empress-Mother Zoe came to power . With her intransigent attitude , she provoked new campaigns by the Bulgarian , involving heavy losses especially for Greece . The position was critical , the army weakened by several bitter defeats .

A man who was of humblest origin and had become an officer in the navy through a brilliant career struck while the iron was hot : Romanos Lekapenos rendered Zoe harmless , married his daughter to Constantine and became co-emperor . Tsar Simeon and his daughter had no chance against the agile upstart who pushed the young Constantine to one side and wanted to found a dynasty of his own . He was the first Emperor who wanted to get to grips with the problem of an over-powerful aristocracy with a law , but drought disasters and epidemics thwarted the success of the measure . In the war with the Bulgarians , he was able to impress with diplomacy and the military , so that in the end Simeon's son married Lekapenos's daughter . Conversely , Byzantium recognised Bulgaria as an independent ecclesiastic area , thus as an autocephalic archdiocese . The peace on the western front released forces for the eastern frontier .

The feudalisation of the themes , i.e. the servitude of the erstwhile military farmers who were no longer soldiers , and the absolute power of the nobles in their sector , took their course and undermined the state . After 200 years , the dynasty of the Macedonians became extinct with the death of Theodora in 1056 and officials took over the throne .