Darius the Great was a king of the Persian Empire who ruled from 522 to 486 BCE. He is known for expanding the empire to its greatest extent, which included parts of Egypt, Greece, and India. Darius implemented a system of provinces, called satrapies, to manage the vast territories and improve administration. He is also famous for his construction projects, including the royal city of Persepolis and the Royal Road, which facilitated trade and communication across the empire. Darius promoted the use of a standardized currency and encouraged cultural exchange, helping to unify the diverse peoples under his rule.