Des Knaben Wunderhorn
The latter part of his life he spent in Regensburg, Frankfurt and Munich, actively engaged in promoting the Catholic faith. Brentano assisted Ludwig Achim von Arnim, his brother-in-law, in the collection of folk-songs forming "Des Knaben Wunderhorn" (1805–1808), which Gustav Mahler drew upon for his song cycle. In 1835, Swiss painter Emilie Linder, painted the famous portrait of him. He died in Aschaffenburg.