Before he could join Banner, however, Altringer had forced the line of the Lech, and had received reinforcements strong enough to neutralize the aid brought to Banner by Horn.

Deeming it necessary above all things to bar the future progress of the enemy, Horn sent orders to Otto Ludwig to join him with all the troops still remaining in Alsace; but finding himself still unable to resist the advance of Altringer, he despatched an urgent request to Duke Bernhard, who had captured Bamberg and the strong places of Kronach and Hochstadt in Franconia, to come to his assistance.

The duke at once quitted Bamberg and marched southward, swept a strong detachment of the Bavarian army under John of Werth from his path, and pressing on reached Donauwurth in March 1633.
Malcolm had rejoined his regiment, which was with Duke Bernhard, just before it advanced from Bamberg and was received with a hearty welcome by his comrades, from whom he had been separated nine months, having quitted them three months before the battle of Lutzen.
The officers were full of hope that Duke Bernhard was going to strike a great blow.

Altringer was away on the shore of Lake Constance facing Horn, Wallenstein was in Bohemia.

Between Donauworth and Vienna were but the four strong places of Ingolstadt, Ratisbon, Passau, and Linz.
Ingolstadt was, the duke knew, commanded by a traitor who was ready to surrender.