The Persians for a certain period possessed a great rule and dominion, but so often as they ventured to overstep the boundaries of Asia they imperilled not only the security of this empire, but their own existence. The Lacedaemonians, after having for many years disputed the hegemony of Greece, at length attained it but to hold it uncontested for scarce twelve years. The Macedonian rule in Europe extended but from the Adriatic region to the Danube, which would appear a quite insignificant portion of the continent. Subsequently, by overthrowing the Persian empire they became supreme in Asia also. But though their empire was now regarded as the greatest geographically and politically that had ever existed, they left the larger part of the inhabited world as yet outside it. For they never even made a single attempt to dispute possession of Sicily, Sardinia, or Libya, and the most warlike nations of Western Europe were, to speak the simple truth, unknown to them. But the Romans have subjected to their rule not portions, but nearly the whole of the world and possess an empire which is not only immeasurably greater than any which preceded it, but need not fear rivalry in the future. In the course of this work it will become more clearly intelligible by what steps this power was acquired, and it will also be seen how many and how great advantages accrue to the student from the systematic treatment of history.
— POLYBIUS