Constantine the Great

Born in 272 in Naissus to a low-born Greek mother and an army officer who would become emperor, Constantine rose through the ranks under Diocletian and Galerius, fighting Persians in the east and campaigning in Britannia with his father. When his father died in 306, the army proclaimed him augustus at York. He spent the next eighteen years in civil war, defeating rival emperors Maxentius and Licinius to claim sole rule by 324. As emperor he restructured the government, introduced the solidus gold coin that anchored currency for a millennium, disbanded the Praetorian Guard, and reorganized the army into mobile strike forces and frontier garrisons. He lived most of his life as a pagan before favouring Christianity in 312 and being baptised on his deathbed by an Arian bishop in 337. The Edict of Milan in 313 ended Christian persecution; the First Council of Nicaea in 325 produced the creed that defined orthodoxy. He rebuilt Byzantium as Constantinople and made it the imperial seat, leaving an empire that would pass to his sons and, through the eastern half, endure another thousand years.