Thucydides, History of the Peloponnesian War
Benjamin Jowett, Ed.

71. In the face of such an enemy, Lacedaemonians, you persist in doing nothing. You do not¹ see that peace is best secured by those who use their strength justly, but whose attitude shows that they have no intention of submitting to wrong. Justice with you seems to consist in giving no annoyance to others and² in defending yourselves only against positive injury³. [2] But this policy would hardly be successful, even if your neighbours were like yourselves; and in the present case, as we pointed out just now, your ways compared with theirs are old-fashioned. [3] And, as in the arts, so also in politics, the new must always prevail over the old. In settled times the traditions of government should be observed: but when circumstances are changing and men are compelled to meet them, much originality is required. The Athenians have had a wider experience, and therefore the administration of their state unlike yours has been greatly reformed. [4] But here let your procrastination end; send an army at once into Attica and assist your allies, especially the Potidaeans, to whom your word is pledged⁴. Do not betray friends and kindred into the hands of their worst enemies; or drive us in despair to seek the alliance of others; [5] in taking such a course we should be doing nothing wrong either before the Gods who are the witnesses of our oaths, or before men whose eyes are upon us. For the true breakers of treaties⁵ are not those who, when forsaken, turn to others, but those who forsake allies whom they have sworn to defend. [6] We will remain your friends if you choose to bestir yourselves; for we should be guilty of an impiety if we deserted you without cause; and we shall not easily find allies equally congenial to us. [7] Take heed then: you have inherited from your fathers the leadership of Peloponnesus; see that her greatness suffers no diminution at your hands.