In the comments on Moreau's operations in Germany, it has already been remarked that it is always a dangerous operation to attempt a concentration upon some designated place within the enemy's lines, for, as a rule, the enemy can mass his forces there more rapidly than the commander of an invading army; that in fact many a campaign has failed because the commanding general has attempted to concentrate his scattered forces upon some point within the territory held by the enemy. By so doing he gives the enemy a chance to assemble his forces between the separated columns of the attacking army, and to bring superior numbers against each column in succession. Yet in these operations Bonaparte not only committed this error, not only did what he had condemned Moreau for doing, but he also violated the principle which he himself had so often set forth and had so often exemplified, namely, _not to invade a country with a double line of operations_. Why then did Bonaparte take this course? To answer satisfactorily this question it is necessary to bear in mind that, at this time, Suchet was fighting greatly superior forces on the Var, and that Masséna was in desperate straits at Genoa. The problem before Bonaparte was not merely to assemble his forces in the vicinity of Milan, but so to assemble them there as to stop the projected invasion of France and bring speedy relief to Masséna. The most direct route from Lake Geneva to Milan is by way of the Great St. Bernard Pass, and thence through northern Italy. Had, therefore, Bonaparte taken the longer route through Switzerland by way of the St. Gothard, the Austrians, in the meantime, could have forced the crossings of the Var, and have compelled Masséna to surrender. Indeed, these events were the more likely to happen, inasmuch as the Army of Reserve, during its march through Switzerland, would not threaten in the least the Austrian communications. The importance of crossing the Great St. Bernard with the Army of Reserve is seen in the fact that no sooner had French troops appeared in the valley of the Aosta than Melas at once withdrew ten thousand men from Suchet's front and ordered them to march on Turin. Thus, by the mere crossing of the Great St. Bernard with the Army of Reserve, the projected invasion of France was brought to an end. It was inevitable that such should be the case; for as soon as the French appeared in the extreme northern part of Italy, their mere presence there threatened the communications of the Austrians. It was therefore necessary that Melas should abandon the invasion of France, in order to destroy, if possible, the French troops that were threatening his rear. In war, it will ever be thus. No commander can afford to take the risk of pushing forward to new conquests so long as his communications are seriously threatened by his enemy.