Adam Clarke on Joshua 6:14

So they did six days - It is not likely that the whole Israelitish host went each day round the city. This would have been utterly impossible: the fighting men alone amounted to nearly 600,000, independently of the people, who must have amounted at least to two or three millions; we may therefore safely assert that only a select number, such as was deemed necessary for the occasion, were employed. Jericho could not have been a large city: and to reduce it could not have required a hundredth part of the armed force under the command of Joshua.