The empire known for using the postal system extensively across its territories was the Persian Empire. Under the rule of Darius the Great in the 5th century BCE, the Persians established a sophisticated courier system called the "Angarium." This network utilized a series of mounted messengers, who could traverse vast distances quickly, effectively facilitating communication across its expansive territories. The system contributed significantly to the administration of the empire, allowing for the efficient exchange of information and the rapid relay of royal edicts. It is considered one of the earliest examples of an organized postal system in history, influencing future postal services in various cultures.