Alexander was certainly much in need of sound guidance. Though Scharnhorst had pointed out the way of salvation, a strategic tempter was soon at hand in the person of General von Phull, an uncompromising theorist who planned campaigns with an unquestioning devotion to abstract principles. Untaught by the catastrophes of the past, Alexander once more let his enthusiasm for theories and principles lead him to the brink of the abyss. Phull captivated him by setting forth the true plan of a defensive campaign which he had evolved from patient study of the Seven Years' War. Everything depended on the proper selection of defensive positions and the due disposition of the defending armies. There must be two armies of defence, and at least one great intrenched camp. One army must oppose the invader on a line near, or leading up to, the camp; while the other army must manoeuvre on his rear or flanks. And the camp must be so placed as to stretch its protecting influence over one, or more, important roads. It need not be on any one of them: in fact, it was better that it should be some distance away; for it thus fulfilled better the all-important function of a "flanking position." Such a position Phull had discovered at Drissa in a curve of the River Dwina. It was sufficiently far from the roads leading from the Niemen to St. Petersburg and to Moscow efficiently to protect them both. There, accordingly, he suggested that vast earthworks should be prepared; for there, at that artificial Torres Vedras, Russia's chief force might await the Grand Army, while the other force harassed its flank or rear.[259] Napoleon had not probed this absurdity to its inmost depths: but he early found out that the Russians were in two widely separated armies; and this sufficed to decide his movements and the early part of the campaign. Having learnt that one army was near Vilna, and the other in front of the marshes of the Pripet, he sought to hold them apart by a rapid irruption into the intervening space, and thereafter to destroy them piecemeal. Never was a visionary theory threatened by a more terrible realism. For Napoleon at midsummer was mustering a third of a million of men on the banks of the Niemen, while the Russians, with little more than half those numbers as yet available for the fighting-line, had them spread out over an immense space, so as to facilitate those flanking operations on which Phull set such store.[260]