Gustavus, who had taken a great fancy to the young Scotch officer, whose spirit of adventure and daring were in strong harmony with his own character, appointed him to ride on his own personal staff.

Although he parted with regret from his comrades, Malcolm was glad to accompany the king on his northward march, for there was no probability of any very active service in Bavaria, and it was certain that a desperate battle would be fought when Gustavus and Wallenstein met face to face in the open field.
At Erfurt Gustavus was joined by Duke Bernhard of Saxe-Weimar with his force, which raised his army to a strength of 20,000.

The news of his approach had again revived the courage of the Elector of Saxony, who had occupied the only towns where the Elbe could be crossed, Dresden, Torgau, and Wittenberg--he himself, with his main army of 15,000 men, lying at Torgau.

From him Gustavus learned that the Imperial army was divided into three chief corps--that of Wallenstein 12,000 strong, that of Pappenheim 10,000, those of Gallas and Holk united 16,000, making a total of 38,000 men.
So great was the speed with which Gustavus had marched to Erfurt that Wallenstein had received no notice of his approach; and believing that for some time to come he should meet with no serious opposition, he had on the very day after the Swedes reached Erfurt despatched Gallas with 12,000 men into Bohemia.

A division of his troops was at the same time threatening Naumburg, whose possession would enable him to block the only easy road with which Gustavus could enter the country held by him.
But Gustavus at Erfurt learned that Naumburg had not yet fallen, and marching with great rapidity reached the neighbourhood of that town before the Imperialists were aware that he had quitted Erfurt, and cutting up a small detachment of the enemy who lay in his way, entered the town and at once began to intrench it.