This defection left the rebels powerless.  Duke Ernst was arrested and imprisoned on a charge of high treason.  Eudolf was exiled.  Werner, who took refuge in his castle, was besieged there by the imperial troops, against whom he valiantly defended himself for several months.  At length, however, finding that his stronghold was no longer tenable, he contrived to make his escape, leaving the nest to the imperialists empty of its bird.

Three years Ernst remained in prison.  Then Conrad restored him to liberty, perhaps moved by the appeals of his mother Gisela, and promised to restore him to his dukedom of Swabia if he would betray the secret of the retreat of Werner, who was still at large despite all efforts to take him.

This request touched deeply the honor of the deposed duke.  It was much to regain his ducal station; it was more to remain true to the fugitive who had trusted and aided him in his need.

“How can I betray my only true friend?” asked the unfortunate duke, with touching pathos.

His faithfulness was not appreciated by the emperor and his nobles.  They placed Ernst under the ban of the empire, and thus deprived him of rank, wealth, and property, reducing him by a word from high estate to abject beggary.  His life and liberty were left him, but nothing more, and, driven by despair, he sought the retreat of his fugitive friend Werner, who had taken refuge in the depths of the Black Forest.

Here the two outlaws, deprived of all honest means of livelihood, became robbers, and entered upon a life of plunder, exacting contributions from all subjects of the empire who fell into their hands.  They soon found a friend in Adalbert of Falkenstein, who gave them the use of his castle as a stronghold and centre of operations, and joined them with his followers in their freebooting raids.

For a considerable time the robber chiefs maintained themselves in their new mode of life, sallying from the castle, laying the country far and wide under contribution, and returning to the fortress for safety from pursuit.  Their exactions became in time so annoying, that the castle was besieged by a strong force of Swabians, headed by Count Mangold of Veringen, and the freebooters were closely confined within their walls.  Impatient of this, a sally in force was made by the garrison, headed by the two robber chiefs, and an obstinate contest ensued.  The struggle ended in the death of Mangold on the one side and of Ernst and Werner on the other, with the definite defeat and dispersal of the robber band.

Thus ended an interesting episode of mediaeval German history.  But the valor and misfortunes of Duke Ernst did not die unsung.  He became a popular hero, and the subject of many a ballad, in which numerous adventures were invented for him during his career as an opponent of the emperor and an outlaw in the Black Forest.  For the step-son of an emperor to be reduced to such a strait was indeed an event likely to arouse public interest and sympathy, and for centuries the doings of the robber duke were sung.