Final answer:
The Pax Romana was initiated by Octavian becoming the ruler of Rome and the Romans discovering concrete.
Explanation:
The events that led to the Pax Romana were:
- Octavian becoming the ruler of Rome: Formed the Second Triumvirate, defeated Caesar's assassins, and eventually won the Battle of Actium to become Augustus in 27 BCE.
- The Romans discovering concrete: Contributed to the empire's infrastructure development, aiding in the growth and stability of the Roman territories.
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