13. The Use of Spies
Whether the object be to crush an army, to storm a city, or to assassinate an individual, it is always necessary to begin by finding out the names of the attendants, the aides-de-camp,
Literally "visitors", is equivalent, as Tu Yu says, to "those whose duty it is to keep the general supplied with information," which naturally necessitates frequent interviews with him.
and door-keepers and sentries of the general in command. Our spies must be commissioned to ascertain these.
As the first step, no doubt towards finding out if any of these important functionaries can be won over by bribery.