History of the Peloponnesian War
Thucydides
Thucydides, Vol. 1-4. Smith, Charles Foster, translator. London and Cambridge, MA: Heinemann and Harvard University Press, 1919-1923.
It is but right, therefore, that we neither should show ourselves worse men than our fathers nor wanting to our own fame. For all Hellas is stirred by this enterprise of ours, and fixes her gaze upon it, and being friendly to us on account of their hatred of the Athenians hopes that we shall succeed in carrying out our designs.
Therefore, even if some of us may think that we are going against them with superior numbers and that in all likelihood the enemy will not risk a pitched battle with us, we must not on that account be a whit less carefully prepared when we advance, but rather must officer and soldier of every state for his own part be always expecting to encounter some danger.
For the events of war cannot be foreseen, and attacks are generally sudden and furious; and oftentimes a smaller force, made cautious by fear, overmatches a larger number that is caught unprepared because it despises the foe.
One should, however, when campaigning in an enemy's country always be bold in spirit, but in action cautious and therefore prepared. For thus men will be most valorous in attacking their opponents and most secure against assault. "And we are going against a city which is not so powerless to defend itself as some may think, but is perfectly prepared in all respects;
we have therefore every reason to expect them to risk a battle, if they have not already set out before we are yet there, at any rate when they see us in their territory laying it waste and destroying their property.