Before the 4th century BC, Macedonia was a small kingdom outside of the area dominated by the great city-states of Athens, Sparta and Thebes, and briefly subordinate to Achaemenid Persia. During the reign of the Argead king PhilipII (359–336 BC), Macedonia subdued mainland Greece and the Thracian Odrysian kingdom through conquest and diplomacy. With a reformed army containing phalanxes wielding the "sarissa" pike, PhilipII defeated the old powers of Athens and Thebes in the Battle of Chaeronea in 338BC. PhilipII's son Alexander the Great, leading a federation of Greek states, accomplished his father's objective of commanding the whole of Greece when he destroyed Thebes after the city revolted. During Alexander's subsequent campaign of conquest, he overthrew the Achaemenid Empire and conquered territory that stretched as far as the Indus River. For a brief period, his empire was the most powerful in the world – the definitive Hellenistic state, inaugurating the transition to a new period of Ancient Greek civilization. Greek arts and literature flourished in the new conquered lands and advances in philosophy, engineering, and science spread throughout much of the ancient world. Of particular importance were the contributions of Aristotle, tutor to Alexander, whose writings became a keystone of Western philosophy.