How did the royal road benefit the persians?

The Royal Road helped the Persian Empire by uniting the empire, delivering mail, and promoted trade and business throughout the empire. When the Royal Road united the empire everything started to happen, the delivered mail and the promotion of trade and business. The Royal Road was for government purposes. When they mailed letters, which needed a new horse every 15 miles, it took 7 days. The promotion letters, which needed a new horse every 15 miles, it took 7 days. The promotion of trade and business was huge, it allowed the Persians to get more money. 

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