It was of the utmost importance that Gustavus should strengthen his friends and overawe the waverers by the approach of his army.

Hitherto Franconia and the Rhine provinces had been entirely in the hands of the Imperialists, and it was needful that a counterbalancing influence should be exerted.

These considerations induced Gustavus to abandon the tempting idea of a march upon Vienna.
The Elector of Saxony was charged with carrying the war into Silesia and Bohemia, the Electors of Hesse and Hesse-Cassel were to maintain Lower Saxony and Westphalia, and the Swedish army turned its face towards the Rhine.
On the 20th of September it arrived before Erfurt, an important fortified town on the Gera, which surrendered at discretion.

Gustavus granted the inhabitants, who were for the most part Catholics, the free exercise of their religion, and nominated the Duke of Saxe-Weimar to be governor of the district and of the province of Thuringen, and the Count of Lowenstein to be commander of the garrison, which consisted of Colonel Foulis's Scottish regiment, 1500 strong.
Travelling by different routes in two columns the army marched to Wurtzburg, the capital of Franconia, a rich and populous city, the Imperialist garrison having withdrawn to the strong castle of Marienburg, on a lofty eminence overlooking the town, and only separated from it by the river Maine.

The cathedral at Wurtzburg is dedicated to a Scottish saint, St.Kilian, a bishop who with two priests came from Scotland in the year 688 to convert the heathen of Franconia.