History of the Peloponnesian War
Thucydides
Thucydides. History of the Peloponnesian War. Crawley, Richard, translator. London and Toronto: J. M. Dent and Sons Ltd.; New York: E. P. Dutton and Co., 1914.
We ought not then to show ourselves inferior to our ancestors, or unequal to our own reputation. For the hopes and attention of all Hellas are bent upon the present effort, and its sympathy is with the enemy of the hated Athens.
Therefore, numerous as the invading army may appear to be, and certain as some may think it that our adversary will not meet us in the field, this is no sort of justification for the least negligence upon the march; but the officers and men of each particular city should always be prepared for the advent of danger in their own quarters.
The course of war cannot be foreseen, and its attacks are generally dictated by the impulse of the moment; and where overweening self-confidence has despised preparation, a wise apprehension has often been able to make head against superior numbers.
Not that confidence is out of place in an army of invasion, but in an enemy's country it should also be accompanied by the precautions of apprehension: troops will by this combination be best inspired for dealing a blow, and best secured against receiving one.
In the present instance, the city against which we are going, far from being so impotent for defence, is on the contrary most excellently equipped at all points; so that we have every reason to expect that they will take the field against us, and that if they have not set out already before we are there, they will certainly do so when they see us in their territory wasting and destroying their property.