 As emperor , Constantine enacted many administrative , financial , social , and military reforms to strengthen the empire . The government was restructured and civil and military authority separated . A new gold coin , the solidus , was introduced to combat inflation . It would become the standard for Byzantine and European currencies for more than a thousand years . The first Roman emperor to claim conversion to Christianity , Constantine played an influential role in the proclamation of the Edict of Milan in 313 , which decreed tolerance for Christianity in the empire . He called the First Council of Nicaea in 325 , at which the Nicene Creed was professed by Christians . In military matters , the Roman army was reorganised to consist of mobile field units and garrison soldiers capable of countering internal threats and barbarian invasions . Constantine pursued successful campaigns against the tribes on the Roman frontiers — the Franks , the Alamanni , the Goths , and the Sarmatians — even resettling territories abandoned by his predecessors during the turmoil of the previous century . 
