The frontiers of states are either large rivers, or chains of mountains, or deserts. Of all these obstacles to the march of an army, the most difficult to overcome is the desert; mountains come next, and broad rivers occupy the third place. NOTE. Napoleon, in his military career, appears to have been called upon to surmount every difficulty which can occur in wars of invasion. In Egypt he traversed deserts, and vanquished and destroyed the Mamelukes, so celebrated for their address and courage. His genius knew how to accommodate itself to all the dangers of this distant enterprise, in a country ill adapted to supply the wants of his troops. In the conquest of Italy, he twice crossed the Alps by the most difficult passes, and at a season, too, which rendered this undertaking still more formidable. In three months he passed the Pyrenees, defeated and dispersed four Spanish armies. In short, from the Rhine to the Borysthenes, no natural obstacle could be found to arrest the rapid march of his victorious army. MAXIM II. In forming the plan of a campaign, it is requisite to foresee everything the enemy may do, and to be prepared with the necessary means to counteract it. Plans of campaign may be modified _ad infinitum_ according to circumstances--the genius of the general, the character of the troops, and the topography of the theatre of action. NOTE. Sometimes we see a hazardous campaign succeed, the plan of which is directly at variance with the principles of the art of war. But this success depends generally on the caprice of fortune, or upon faults committed by the enemy--two things upon which a general must never count. Sometimes the plan of a campaign, although based on sound principles of war, runs the risk of failing at the outset if opposed by an adversary who acts at first on the defensive, and then, suddenly seizing the initiative, surprises by the skilfulness of his manœuvres. Such was the fate of the plan laid down by the Aulic council for the campaign of 1796, under the command of Marshal Wurmser. From his great numerical superiority, the marshal had calculated on the entire destruction of the French army, by cutting off its retreat. He founded his operations on the defensive attitude of his adversary, who was posted on the line of the Adige, and had to cover the siege of Mantua, as well as central and lower Italy.