These were the questions to which Marlborough was preparing to give an answer in the summer of 1704. He had conceived the brilliant plan of moving the whole of his army, except the Dutch, from the field of operations in the Netherlands to a totally new base upon the upper Danube, and of crushing Marsin and the elector before Tallard could come to their help from the Rhine, or Villeroy overtake him from the Meuse. It was a scheme which was certain to fail except in the hands of a consummate general, for it involved not merely a victory over equal and possibly superior forces, but a long and extremely hazardous flank march over difficult country, and a race against time. And that was not all, for before he could even undertake it, he had to deceive the Dutch and lull Villeroy into a false security. If the Dutch once suspected that he was going to move his army away from the protection of their frontier, they would impose an energetic and decided veto. If Villeroy once divined that Marlborough was engaged in making a long march up the Rhine, he could ruin the whole plan in a moment by a well-directed flank attack. To surmount these difficulties, Marlborough, keeping his real plan an absolute secret, let it be generally known that he intended to try and turn the lines and fortresses of the Netherlands, by advancing into France by way of the Moselle, and he publicly asked for, and obtained, the permission of the Dutch to that scheme. This enabled him to summon the Brandenburg contingent to the Rhine at Mainz, and to move his own headquarters to Coblentz without incurring suspicion, and to leave Overkirk with the Dutch army and the Dutch deputies at Maestricht on his extreme right, to guard the line of the Meuse should Villeroy advance on Amsterdam during his absence. The plan succeeded admirably. Villeroy, completely deceived, took up a strong position on the upper Moselle near Trier to resist the advance of the allies, and waited in vain for the first signs of the invading army. [Sidenote: =His flank march to the Danube.=] The Dutch left behind at Maestricht could not interfere with Marlborough’s plans. All was ready.[8] In June 1704 he threw off the mask, advanced up the Rhine by forced marches to Mainz, then, picking up the Brandenburg contingent as he went, he left the Rhine and directed his army straight upon the upper Danube at Donauwörth. At Heilbronn he was joined by a German force, and near Ulm by prince Eugene and prince Louis of Baden. It was agreed that Eugene should return to Stolhofen to prevent Tallard, and possibly Villeroy if he appeared upon the scene, from coming to the assistance of the elector and Marsin before the allies could attack them. Marlborough himself and prince Louis of Baden marched straight against the elector, who had entrenched himself on the Schellenberg near Donauwörth, carried the lines by assault on the 2d of July and drove the elector back on Augsburg, thus thrusting themselves in