The first thing was to gain over the Elector of Bavaria. The Court of Vienna, seeking to persuade or compel that prince to join the Coalition, made overtures (September 3rd to 6th) with which he dallied for a day or two until an opportunity came of escaping to the fortress of Würzburg. Mack thereupon crossed the River Inn and sought, but in vain, to cut off the Bavarian troops from that stronghold. Accordingly, the Austrian leader marched on to Ulm, where he arrived in the middle of September; and, not satisfied with holding this advanced position, he pushed on his outposts to the chief defiles of the Black Forest, while other regiments held the valley of the River Iller and strengthened the fortress of Memmingen. Doubtless this would have been good strategy, had his forces been equal in numbers to those of Napoleon. At that time the Black Forest was the only physical barrier between France and Southern Germany; the Rhine was then practically a French river; and, only by holding the passes of that range could the Austrians hope to screen Swabia from invasion on the side of Alsace. [Illustration: BATTLE OF ULM] But Mack forgot two essential facts. Until the Russians arrived, he was too weak to hold so advanced a position in what was hostile ground, now that Bavaria and the other South German States obeyed Napoleon's summons to range themselves on his side. Further, he was dangerously exposed on the north, as a glance at the map will show. Ulm and the line of the Iller formed a strong defence against the south-west: but on the north that position is singularly open: it can be turned from the valleys of the Main, the Neckar, and the Altmühl, all of which conduct an invader to the regions east of Ulm. Indeed, it passes belief how even the Aulic Council could have ignored the dangers of that position. Possibly the fact that Ulm had been stoutly held by Kray in 1796 now induced them to overrate its present importance; but at that time the fortified camp of Ulm was the central knot of vast operations, whereas now it was but an advanced outpost.[24] If Francis and his advisers were swayed by historical reminiscences it is strange that they forgot the fate of Melas in Piedmont. The real parallel had been provided, not by Kray, but by the general who was cut off at Marengo. Indeed, in its broad outlines, the campaign of Ulm resembles that of Marengo. Against foes who had thrust their columns far from their base, Napoleon now, as in 1800, determined to deal a crushing blow. On the part of the Austrians we notice the same misplaced confidence, the same lack of timely news, and the same inability to understand Napoleon's plan until his dispositions are complete; while his strategy and tactics in 1805 recall to one's mind the masterly simplicity of design, the subtlety and energy of execution, which led up to his triumph in the plains of Piedmont.