History of the Peloponnesian War

Nevertheless; we have not been brought to this by any decay in our power, or through having our heads turned by aggrandizement; no, our resources are what they have always been, and our error has been an error of judgment, to which all are equally liable.

Accordingly the prosperity which your city now enjoys, and the accession that it has lately received, must not make you fancy that fortune will be always with you.

Indeed sensible men are prudent enough to treat their gains as precarious, just as they would also keep a clear head in adversity, and think that war, so far from staying within the limit to which a combatant may wish to confine it, will run the course that its chances prescribe; and thus, not being puffed up by confidence in military success, they are less likely to come to grief, and most ready to make peace, if they can, while their fortune lasts.