Scholar of Sicilian medieval architecture. While a student at the Technische Hochschule, Dresden he travelled to Sicily in 1910 to study the architecture of four small towns, Castrogiovanni (today known as Enna), Piazza Armerina, Nicosia and Randazzo, in order to trace the influence of Lombardic culture in the indigenous architecture. His dissertation, published in 1917, was on that very topic (Passalacqu). Leopold's Ph.D. advisors were the medievalist Hugo Hartung (1855-1932), art historian Cornelius Gurlitt and Robert Bruck (b. 1863). Leopold photographed many of the monuments of Sicily, documenting their appearance before modern re-arrangement of the cities.
[dissertation:] Sizilianische Bauten des Mittelalters, in Castrogiovanni, Piazza Armerina, Nicosia und Randazzo. Berlin: E. Wasmuth, 1917 https://catalog.hathitrust.org/Record/010249817;
Passalacqu, Francesca. "Alla ricerca del Medioevo lombardo: il viaggio-studio di Walter Leopold in Sicilia orientale." in Degli Aspetti dei Paesi (exhibition catalog) CIRICE 2016, pp. 937-946, https://www.academia.edu/30702072/Alla_ricerca_del_Medioevo_lombardo_il_viaggio-studio_di_Walter_Leopold_in_Sicilia_orientale_in_Degli_Aspetti_dei_Paesi_a_cura_di_A._Berrino_A._Buccaro_e-book_CIRICE_2016_pp._937-946.