In 1386 Peter of Thornberg supported the Habsburgs against the city of Bern in the Sempach War. During the war, Bernese troops attacked Koppigen Castle and burned it to the ground. In 1397, Peter of Thornberg, the last of the line, died. He left all his possessions in Koppigen to the newly established Carthusian Charterhouse of Thornberg, which he had founded shortly before. The Carthusians made Koppigen the center of a parish that included Hellsau, Alchenstorf, Höchstetten and Willadingen. After the Protestant Reformation, in 1528, Bern secularized the Charterhouse and all of its possessions. Bern placed a vogt and a high court in Koppigen and it became part of the district of Burgdorf.