The 4th through 7th centuries are often considered periods of decay and decline for the Roman Empire. I view them, however, as times of crisis and regeneration, as the previously pagan Empire was transformed into an amazingly resilient Christian Empire which persisted for another millennium despite attacks on all sides and myriad convulsions from within. Who were the most effective rulers during this period? Opinions vary, but here are my choices. Portraits of all, taken from antiquity, may be found in the above image: Constantine the Great (AD 306-337). Constantine may be considered the founder of the Christian Roman...