Final answer:
The Battle of the Milvian Bridge in 312 CE was the pivotal event at which Emperor Constantine defeated Maxentius to become the sole emperor of Rome, leading to political unification and the legalization of Christianity.
Step-by-step explanation:
At the Battle of the Milvian Bridge in 312 CE, Emperor Constantine defeated his principal rival Maxentius. This crucial victory led Constantine to take over as the sole emperor of Rome.
Following his father's death in 306, Constantine was declared Augustus by his father's troops in Eboracum (York, England). Civil wars ensued, culminating in his march from Britannia to Italy, where the pivotal battle against Maxentius occurred. After this significant victory, Constantine continued to unify Rome under his rule, eventually overcoming Licinius in 324 CE and concluding his quest for sole rulership.
During his reign, Constantine not only re-established stability within the Roman Empire and legalized Christianity but also initiated large building projects in Rome and moved the capital to Constantinople, influencing the future trajectory of the empire.