The empire that was at its height during the reign of Augustus Caesar is the Roman Empire. Augustus, originally known as Octavian, was the first Roman emperor, ruling from 27 BC until his death in AD 14. His reign marked the transition from the Roman Republic to the Roman Empire, characterized by significant territorial expansion, extensive infrastructure development, and the establishment of relative peace known as the Pax Romana. Under Augustus, the empire flourished economically and culturally, solidifying Rome's dominance in the Mediterranean. His reign laid the foundation for subsequent emperors and significantly shaped the course of Western history.