When Constantine remained the sole emperor, he decided to move the capital from Rome to Constantinople, the old Megara colony called Byzantis or Byzantium. The move of a state that was Roman in administration, language and legal system to a location under the cultural influence of Hellenism and oriental peoples, determined the change in its whole substance. Constantine's contribution to the administrative reorganization of the state and his religious policy are important historical factors as they set the foundations for the future development of Byzantium. The elimination of many of his political adversaries - even members of his family - in 326 is notable yet unaccountable due to lack of historical sources.

As far as the Empire boundaries were concerned, Constantine did not make any efforts to expand. He simply ensured the integrity of the Empire by posting his sons at the frontier fronts. He successfully dealt with barbaric tribe attacks on the Rhine and the Danube; he even managed to strike peace with the Goths, whereby they were expected to protect the Danube border, receiving food and money in return. In the East, Constantine's religious policy provoked the Persians, who responded by prosecutions of their Christian subjects.