He had been joined by Maximilian of Bavaria, and his force amounted to 40,000 men.
Gustavus gave his army four days' rest at Donauworth, and then advanced with 32,000 men against the Lech.

His dragoons, who had been pushed forward, had found the bridges destroyed.

He first attempted to repair that at Rain, but the fire of the artillery and musketry was so heavy that he was forced to abandon the idea.

He then made a careful reconnaissance of the river, whose course was winding and erratic.
Finding that at every point at which a crossing could be easily effected Tilly's batteries and troops commanded the position, he determined to make his attack at a point where the river made a sharp bend in the form of a semicircle, of which he occupied the outer edge.

He encamped the bulk of his army at the village of Nordheim, a short distance in the rear, and erected three powerful batteries mounting seventy-two guns.
One of these faced the centre of the loop, the others were placed opposite the sides.
The ground on the Swedish bank of the river was higher than that facing it; and when the Swedish batteries opened they so completely swept the ground inclosed by the curve of the river that the Imperialists could not advance across it, and were compelled to remain behind a rivulet called the Ach, a short distance in the rear of the Lech.