Civil War Climax: Adrianople and Chrysopolis; Constantine Sole Augustus

Eight years after Cibalae, the war ended where continents meet. In the summer and autumn of 324, Constantine drove Licinius from Thrace to the straits, winning first near Adrianople and then decisively at Chrysopolis, opposite Byzantium. The geography forced choices: hold the landward approaches, or contest the crossings. Constantine did both [14][10].

At Adrianople, the Balkan road network funneled armies into collision. Constantine’s troops, toughened by campaigns in Pannonia and Italy, broke Licinius’s formations and sent them reeling toward the Hellespont. The victory opened the route to the straits. The creak of oarlocks soon joined the clang of swords as Constantine assembled transports on the Propontis and Hellespont [14][10].

Chrysopolis decided the matter. Under an azure sky and a whipping sea wind, Constantine ferried men across the Bosporus from Europe to Asia. The currents ran hard; pilots hugged the Asian shore. Licinius tried to block and then to meet the landing, but Constantine’s veterans formed fast. Scarlet standards snapped, and the push drove Licinius’s lines into disorder. When the rout came, it ran all the way to Nicomedia [14][10].

Licinius capitulated. Constantine spared him initially—political theater that ended with Licinius’s later execution—but the war was over. The Tetrarchy, already frayed, finally snapped. Constantine, at last sole Augustus, controlled Rome, the Danube, and the east’s great cities: Nicomedia, Antioch, Alexandria. From the Bosporus he looked both directions and saw an empire to refashion [14][10].

The battles altered more than titles. They shifted the empire’s center of gravity. Byzantium, battered in the fighting and strategically perfect, stood out as a potential capital. Within months, work would begin to turn its walls, fora, and harbors into Nova Roma—Constantinople. The sounds of war would give way to hammers, and the glint of steel to porphyry and marble [13][15][10].