In 1879 he founded the Aachener Geschichtsverein, and having spent his concluding years at Bonn and at Aix-la-Chapelle, he died in the latter city on 27 April 1887.
On the history of Florence and of Tuscany he wrote Tavole cronologiche e sincrone della storia fiorentina (1841; Supplement, 1875); Geschichte Toscanas seit dem Ende des florentinischen Freistaats (History of Toscany since the end of the Florentine freestate, Gotha, 1876–77); and a work on Lorenzo de' Medici (Leipzig, 1874, and again 1883).
Turning his attention to the history of Naples, he wrote Die Carafa von Maddaloni Neapel unter spanischer Herrschaft (1851; Eng.
Other works which may be mentioned are Zeitgenossen, Biografien und Charakteristichen (Berlin, 1862); Bibliografia dei lavori pubblicati in Germania sulla storia d'Italia (Berlin, 1863); Biographische Denkblätter nach personlichen Erinnerungen (Biographical memorials from personal memories, Leipzig, 1878); and Saggi di storia e letteratura (Florence, 1880).
gesunden und kranken Tagen (From Frederick William IV's healthy and sick days, Leipzig, 1885).