The line of the Rhine divided the opposing armies. At the outset the French corps crossed the river at Strasburg, Brisach, Bâle, and Schaffhausen. Moreau then attempted to unite these corps before proceeding to attack Kray in force. 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 can the commander of an invading army. In fact, many a campaign has failed because the commanding general has attempted to unite his scattered forces at 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. Thus, when Moreau crossed the Rhine at Strasburg, Brisach, Bâle, and Schaffhausen, he gave Kray the opportunity of defeating in detail the several French corps so widely separated from one another. Though the topography of the country was such that it did not allow Kray to concentrate his forces and throw them readily upon the separated French corps in succession, yet, had he foreseen the design of his adversary, undoubtedly he could have massed his forces between Schaffhausen and Bâle, along the Wutach, and have thus intervened between Lecourbe's corps and that of Moreau. By such a manoeuvre, he would have stood a good chance of crushing both Moreau and St. Cyr, before they could have been re-enforced by either Ste. Suzanne or Lecourbe. Again: Moreau's plan necessitated that his own corps and that of St. Cyr should make long flank marches on the German side of the river. In making these marches, the French corps necessarily exposed their own flanks to the attacks of the enemy. In fact, Kray might have issued in force from the Black Forest, and have attacked both Moreau and St. Cyr with great chances of success. Had he done so, doubtless these two French corps would have been destroyed; for they would have found themselves enclosed between a victorious enemy on one side and an impassable river on the other. Even when protected by a river, or other great natural obstacle, a flank march, in the vicinity of an active enemy, is often a difficult manoeuvre; but when undertaken in an enemy's country, between an unfordable river on one side, and an active enemy on the other, it then becomes an extremely delicate and dangerous operation.