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

18. 'What reason can we give to ourselves for hesitation? what excuse can we make to our allies¹ for denying them aid? We have sworn to them, and have no right to argue that they never assisted us². In seeking their alliance we did not intend that they should come and help us here, but that they should harass our enemies in Sicily, and prevent them from coming hither. [2] Like all other imperial powers, we have acquired our dominion by our readiness to assist any one, whether Barbarian or Hellene, who may have invoked our aid. If we are all to sit and do nothing, or to draw distinctions of race when our help is requested, we shall add little to our empire, and run a great risk of losing it altogether. [3] For mankind do not await the attack of a superior power, they anticipate it. We cannot cut down an empire as we might a household; but having once gained our present position, we must, while keeping a firm hold upon some, contrive occasion against others; for if we are not rulers we shall be subjects. You cannot afford to regard inaction in the same light as others might, unless you impose a corresponding restriction on your practice. [4] Convinced then that we shall be most likely to increase our power here if we attack our enemies there, let us sail. We shall humble the pride of the Peloponnesians when they see that, scorning the delights of repose, we have attacked Sicily. By the help of our acquisitions there, we shall probably become masters of all Hellas; at any rate we shall injure the Syracusans, and at the same time benefit ourselves and our allies. [5] Whether we succeed and remain, or depart, in either case our navy will ensure our safety; [6] for at sea we shall be more than a match for all Sicily. Nicias must not divert you from your purpose by preaching indolence, and by trying to set the young against the old; rather in your accustomed order, old and young taking counsel together, after the manner of your fathers who raised Athens to this height of greatness, strive to rise yet higher. Consider that youth and age have no power unless united; but that the shallower and the more exact and the middle sort of judgment, when duly attempered, are likely to be most efficient. The state, if at rest, like everything else will wear herself out by internal friction. Every pursuit which requires skill will tend to decay, whereas by conflict the city will always be gaining fresh experience and learning to defend herself, not in theory, but in practice. [7] My opinion in short is, that a state used to activity will quickly be ruined by the change to inaction; and that they of all men enjoy the greatest security who are truest to themselves and their institutions even when they are not the best.'