This Marlborough knew. To enter Bavaria, to occupy its towns (only one of which, Ingolstadt, was tolerably fortified), and if possible to take its capital, Munich, had been from its inception the whole business and strategic motive of his march to the Danube.

But if Marlborough desired to enter Bavaria, Donauwörth was the key to Bavaria from the side upon which he was approaching.

This word “key” is so often used in military history, without any explanation of it which may render it significant to the reader, that I will pause a moment to show why Donauwörth might properly be called in metaphor the “key” of Bavaria to one advancing from the north and west.

Bavaria could only be reached by a general coming as Marlborough came, on condition of his possessing and holding some crossing-place over the Danube, for Marlborough’s supplies lay north of that river (principally at Nördlingen), and the passing of the enormous supply of an army over one narrow point, such as is a bridge over such an obstacle as a broad river, demands full security.

It will further be seen from the map that yet another obstacle, defending Southern Bavaria and its capital towards the west, as the Danube does towards the north, is the river Lech; a passage over this was therefore also of high importance to the Duke of Marlborough and his allies. Now, a man holding Donauwörth can cross both rivers at the same time unmolested, for they meet in its neighbourhood.

Further, Donauwörth was a town amply provisioned, full of warehouse room, and in general affording a good advanced base of supply for any army marching across the Danube. It afforded an opportunity for concentration of supplies, it contained waggons and horses and food. Supplies, it must be remembered, were the great difficulty of each of the two opposed forces, in this moving of great numbers of men east of the Black Forest, in a comparatively poor country, largely heath and forest, and ill populated.

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Map showing how Donauwörth is the key of Bavaria from the North-West.