Constantine the Great vs Ivan III the Great

Constantine defeated his rival Maxentius at the Milvian Bridge near Rome. According to tradition, Constantine saw a vision of a cross in the sky with the words 'In this sign, conquer.' The victory made Constantine the sole ruler of the Western Roman Empire and led to his conversion to Christianity.

Constantine and his co-emperor Licinius issued the Edict of Milan, granting religious toleration to all religions in the Roman Empire, including Christianity. The edict ended the persecution of Christians, restored confiscated church property, and established Christianity as a legally recognized religion.

Constantine defeated his co-emperor Licinius at the battles of Adrianople and Chrysopolis, ending the Tetrarchy system. He became the sole ruler of the entire Roman Empire, reuniting the Western and Eastern halves under his control. This reunification was the last time the Roman Empire was united under a single ruler.

Constantine convened the First Council of Nicaea, the first ecumenical council of the Christian Church, to resolve the Arian controversy over the nature of Christ. The council produced the Nicene Creed, affirming the divinity of Christ and establishing a unified Christian doctrine. Constantine presided over the council.

Constantine dedicated the city of Constantinople (modern Istanbul) as the new capital of the Roman Empire, built on the site of the ancient Greek city of Byzantium. The city was strategically located on the Bosporus strait, controlling trade routes between Europe and Asia. It became the capital of the Eastern Roman Empire for over a thousand years.

Ivan III married Sophia (Zoe) Palaiologina, niece of the last Byzantine emperor. This marriage allowed Ivan to claim succession to the Byzantine Empire, adopt the double-headed eagle as a symbol, and promote Moscow as the Third Rome.

Ivan III conquered the Novgorod Republic after a series of campaigns. He abolished the veche (assembly) and removed the veche bell, incorporating Novgorod's vast territories into the Grand Principality of Moscow.

Ivan III faced the Mongol army of Khan Akhmat across the Ugra River. After weeks of stalemate, the Mongols withdrew without battle. This event ended 240 years of Mongol suzerainty over Russia.

Ivan III promulgated a new legal code, the Sudebnik, which standardized laws across the Russian lands. It restricted peasant mobility by limiting the time for transfer between landowners, a step toward serfdom.

Ivan III launched a war against Lithuania, capturing the cities of Bryansk, Dorogobuzh, and Putivl. The war ended with the Truce of 1503, which ceded significant territories to Moscow.