peculiar to an army, and it is essential to the reading of military history to appreciate these difficulties; for the degrees of impediment which natural features present to thousands upon the march are utterly different from those which they present to individuals or to civilian parties in time of peace. Since it is to difficulties of this latter sort that we are most accustomed by our experience, the student of a campaign will often ask himself (if he is new to his subject) why such and such an apparently insignificant stream or narrow river, such and such a range of hills over which he has walked on some holiday without the least embarrassment, have been treated by the great captains as obstacles of the first moment.