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 Wuerzburg.

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.