How did octavian's rule serve as a transition from roman republic to empire

Before he rose to power, it was the Roman Republic. After his death, it was the Roman Empire. But the time period when he ruled is simply called the Age of Augustus or the Augustan Principate. He created the bridge between Republic to Empire. He reformed the Senate, the military, societal structures and religion. He initiated an extensive building program and shaped and reordered ideology. 

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