The founder of the Achaemenid Empire was King Cyrus II, called 'the Great', who ruled from 559 to 529 BC. After overthrowing the Median king Astyages (his maternal grandfather) in 550 BC Cyrus began to expand his empire.
He attacked the Kingdom of Lydia after its allies, the Babylonians, had been lulled into a period of inactivity. An indecisive battle was fought on the Halys river frontier in 547 BC, after which the Lydians retired to Sardis. Being late in the campaign season, the Lydian king Croesus disbanded his army, but Cyrus surprised him by continuing the war. He took the city, captured the king and then subdued the Greek city states of Ionia in western Anatolia.
In 539 BC, Cyrus usurped the throne of the Babylonians, deposing their king, Nabonidus, virtually without a fight. Cyrus then prepared to invade Egypt, but was called to his eastern frontier to deal with trouble there. After several years of fighting, he was killed in 529 BC in the region of the Oxus and Jaxartes rivers.
