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

11. 'Men of Peloponnesus, and you, allies, many are the expeditions which our fathers made¹ both within and without the Peloponnese, and the veterans among ourselves are experienced in war; and yet we never went forth with a greater army than this. But then we should remember that, whatever may be our numbers or our valour, we are going against a most powerful city. [2] And we are bound to show ourselves worthy of our fathers, and not wanting to our own reputation. For all Hellas is stirred by our enterprise, and her eyes are fixed upon us: she is friendly and would have us succeed because she hates the Athenians. [3] Now although some among you, surveying this great host, may think that there is very little risk of the enemy meeting us in the field, we ought not on that account to advance heedlessly; but the general and the soldier of every state should be always expecting that his own division of the army will be the one first in danger. [4] War is carried on in the dark; attacks are generally sudden and furious, and often the smaller army, animated by a proper fear, has been more than a match for a larger force which, disdaining their opponent, were taken unprepared by him. [5] When invading an enemy's country, men should always be confident in spirit, but they should fear too, and take measures of precaution; and thus they will be at once most valorous in attack and impregnable in defence.

[6] 'And the city which we are attacking is not so utterly² powerless against an invader, but is in the best possible state of preparation,³ and for this reason our enemies may be quite expected to meet us in the field. Even if they have no such intention beforehand, yet as soon as they see us in Attica, wasting and destroying their property, they will certainly change their mind. [7] For all men are angry when they not only suffer but see, and some strange form of calamity strikes full upon the eye; the less they reflect the more ready they are to fight; [8] above all men the Athenians, who claim imperial power, and are more disposed to invade and waste their neighbour's land than to look on while their own is being wasted. [9] Remembering how great this city is which you are attacking, and what a fame you will bring on your ancestors and yourselves for good or evil according to the result, follow whithersoever you are led; maintain discipline and caution above all things, and be on the alert to obey the word of command. It is both the noblest and the safest thing for a great army to be visibly animated by one spirit.'