At last, in June, 1585, he was exchanged, on extremely rigorous terms, for Egmont.

During his captivity in this vile dungeon, he composed not only his famous political and military discourses, but several other works, among the rest; Annotations upon Plutarch and upon the Histories of Guicciardini.
The siege of Groningen proceeded, and Parma ordered some forces under Martin Schenck to advance to its relief.

On the other hand, the meagre states' forces under Sonoy, Hohenlo, Entes, and Count John of Nassau's young son, William Louis, had not yet made much impression upon the city.
There was little military skill to atone for the feebleness of the assailing army, although there was plenty of rude valor.

Barthold Entes, a man of desperate character, was impatient at the dilatoriness of the proceedings.

After having been in disgrace with the states, since the downfall of his friend and patron, the Count De la Marck, he had recently succeeded to a regiment in place of Colonel Ysselstein, "dismissed for a homicide or two." On the 17th of May, he had been dining at Rolda, in company with Hohenlo and the young Count of Nassau.