 As a ruler , Justinian showed great energy . He was known as " the emperor who never sleeps " on account of his work habits . Nevertheless , he seems to have been amiable and easy to approach . Around 525 , he married his mistress , Theodora , in Constantinople . She was by profession a courtesan and some twenty years his junior . In earlier times , Justinian could not have married her because of her class , but his uncle , Emperor Justin I , had passed a law allowing intermarriage between social classes . Theodora would become very influential in the politics of the Empire , and later emperors would follow Justinian 's precedent in marrying outside the aristocratic class . The marriage caused a scandal , but Theodora would prove to be shrewd judge of character and Justinian 's greatest supporter . Other talented individuals included Tribonian , his legal adviser ; Peter the Patrician , the diplomat and longtime head of the palace bureaucracy ; Justinian 's finance ministers John the Cappadocian and Peter <unk> , who managed to collect taxes more efficiently than any before , thereby funding Justinian 's wars ; and finally , his prodigiously talented generals , Belisarius and Narses . 
