Jamieson, Fausset and Brown on Joshua 8:3

3. So Joshua ... chose out thirty thousand mighty men of valour--Joshua despatched thirty thousand men under cover of night, to station themselves at the place appointed for the ambuscade. Out of this number a detachment of five thousand was sent forward to conceal themselves in the immediate precincts of the town, in order to seize the first opportunity of throwing themselves into it [Jos 8:12].