Darius the Great was a king of the Achaemenid Empire, ruling from 522 to 486 BCE. He is known for his administrative genius, expanding the empire to its greatest extent, which included parts of Egypt, Greece, and India. Darius implemented a system of satrapies, or provinces, to manage the vast territories effectively. He is also famous for his construction projects, including the royal city of Persepolis and the Royal Road, which improved communication and trade across the empire. Darius promoted the use of a standardized currency, facilitating economic growth and stability during his reign.