Final answer:
Constantine became sole emperor of the Roman Empire in 324 CE after defeating and executing his co-emperor Licinius. His reign marked a significant period for Christianity, with the Edict of Milan in 313 supporting its spread, and after the decisive Battle of the Milvian Bridge in 312 that cemented his rise to power.
Step-by-step explanation:
Constantine became the sole emperor of the Roman Empire in 324 CE after a power struggle with his co-emperor Licinius. Following his victory over Licinius, he was able to pursue significant building projects, such as the founding of Constantinople, which became the new capital of the Roman Empire. Constantine's reign, from 306 to 337 AD, was a transformative period for Christianity within the empire. His Edict of Milan in 313 granted Christianity the freedom it needed to flourish, leading to its eventual dominance as the state religion.
Constantine's ascension was solidified after defeating Maxentius at the Battle of the Milvian Bridge in 312. The transition to sole ruler was complete when Licinius was executed in 324 CE, ending the civil unrest and unifying the empire. Constantine's conversion to Christianity and his subsequent patronage of the Church marked the beginning of a new era of Christian governance in Rome.