Final answer:
The shift from Roman Republic to Empire was marked by Augustus' rise to power.
Explanation:
The event that marked Rome's shift from a republic to an empire was the rise of Augustus, also known as Octavian. After his victory over Marc Antony, Augustus essentially replaced the republican system with imperial rule, starting the Roman Empire.
Augustus consolidated power and established a new political structure where a single sovereign controlled Rome's vast territories, laying the foundation for the Roman Empire that lasted for centuries.
This transition was significant, as it marked the end of the Roman Republic and the beginning of imperial rule under Augustus, shaping the course of Roman history for years to come.
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