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. [Illustration: Map showing how Donauwörth is the key of Bavaria from the North-West.] No serious permanent defences, such as could delay the capture of the town, surrounded Donauwörth; but up above it lies a hill, called from its shape "the Schellenberg" or "Bell Hill." This hill is not isolated, but joins on the higher ground to its north by a sort of flat isthmus, which is level with the summit or nearly so.[5] The force which, on perceiving the Duke of Marlborough's intention of capturing Donauwörth, the Elector of Bavaria very rapidly detached to defend that town, was under the command of Count d'Arco; it consisted of two regiments of cavalry and about 10,000 infantry (of whom a quarter were French). D'Arco had orders to entrench the hill above the town as rapidly as might be and to defend it from attack; for whoever held the Schellenberg was master of Donauwörth below. But the Elector could only spare eight guns for this purpose from his inferior forces. Upon the 2nd of July, in the early morning, Marlborough, by one of those rapid movements which were a prime element in his continuous success, marched before dawn with something between seven and eight thousand infantry carefully chosen for the task and thirty-five squadrons of horse for the attack on the Schellenberg. It was Marlborough's alternate day of command.