[2] After the death of the archbishop in 1078 at the hands of peasants, Bruno attached himself to Werner of Wolkenburg, Prince-Bishop of Merseburg, to whom, in 1082, he dedicated the work, "De Bello Saxonico" by which he is chiefly known.
[3] Bruno sought to justify the rebellion of the Saxons and the election of the first anti-king, Rudolf, and to show how by his oppressive government King Henry had forfeited any right to rule, both for himself and his dynasty.
Bruno was at pains to stress that this election was conducted with the full knowledge and involvement of a papal legate, and indeed followed the standards of probity laid down by canon law.
The letters to which they refer, which Bruno reproduced in full, were those sent by Gregory in the summer of 1077 to his legates, and to the clergy and people of Germany, setting out the terms by which a judgement might be made between the respective claims of Henry and Rudolf to be the rightful king.
Bruno indeed supported the pope's cause, and his Saxon sympathies manifest themselves at times in his writings, but of his sincerity and his expressed purpose to narrate the truth there can be no doubt.