Answer:
He improved the army and the roads, and created a navy.
Step-by-step explanation:
At that time, Caesar Augustus realized that empire wouldn't be able to thrive based on military alone. Even though he believed security is important, he also believed that enhancing trade is the key for the Roman empire to expand its influence.
This is why he invested a lot in improving streets and aqueducts within the empire. Both of these allowed faster/easier product distributions for merchants who wanted to deliver their products through a long route using carriage or boats. The increase in trade allow more funds that he had under his disposal. He allocate that fund to improve the army and created a navy that increase the empire's protection from attacks through sea routes.