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