The Persians had made it a habit to absorb, after conquest, the individual countries they had vanquished, leaving their internal structures largely intact. Alexander admired the Persian way of administering an empire, as reflected in what he saw in his travels and what he read of the administration of Cyrus the Great. Following Aristotle's advice that a king must balance power between different parties, Alexander began to use a combination of locals, Persians, and Macedonians to rule his growing empire, though he filled key administrative positions with Greeks. Alexander understood the importance of coinage in international transactions. He founded a number of royal mints throughout the empire to facilitate trade, feeding them with the gold reserves of the Persian kings. Alexander, though rich in talents and strengths, had one notable weakness: he was unable to consolidate his empire. Running a stable state was not for him.