Final answer:
The system developed to protect the empire from invading armies was a system of beacons.
Step-by-step explanation:
The system that was developed to help protect the empire from invading armies was a system of beacons. These beacons were strategically placed across the empire and served as a communication network. When an invading army was spotted, the beacons would be lit in sequence to alert the surrounding areas of the impending threat.
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