Antigonus I Monophthalmus vs Constantine the Great

Antigonus I defeated Eumenes, a former general of Alexander, at Gabiene in Persia. This victory eliminated a major rival and gave Antigonus control over the eastern satrapies, making him the most powerful of the Diadochi at that time.

Antigonus I besieged and captured the city of Tyre from Ptolemy I's forces. The siege demonstrated his military capabilities and expanded his control over Phoenicia and Syria, strengthening his position in the Diadochi conflicts.

Antigonus I declared himself king of Asia, claiming authority over the entire former empire of Alexander. This act prompted other Diadochi to also assume royal titles, formalizing the breakup of Alexander's empire into separate Hellenistic kingdoms.

Antigonus I Monophthalmus commanded his army against the allied forces of Seleucus, Lysimachus, and Cassander at Ipsus. He was defeated and killed in battle, ending his ambition to reunite Alexander's empire. His death solidified the division of the empire among the other Diadochi.

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.