Darius I (l. c. 550-486 BCE, r. 522-486 BCE), also known as Darius the Great, was the third Persian King of the Achaemenid Empire. His reign lasted 36 years, from 522 to 486 BCE; during this time the Persian Empire reached its peak.
Darius led military campaigns in Europe, Greece, and even in the Indus valley, conquering lands and expanding his empire. Not only resuming military prowess, Darius also improved the legal and economic system and conducted impressive construction projects across the Persian Empire.
Vast military expeditions marked Darius’ rule. After consolidating his power at home, he set off to secure the lands of Egypt, which had been conquered before by Cambyses, and in 519 BCE he incorporated a large part of Egypt into his empire.
The following year, in 518 BCE, he conquered parts of India, namely northern Punjab as his inscriptions testify. Herodotus adds that India was the 20th satrapy of the empire and also that parts of the Indus valley also fell victim to Persian warfare.