MLA

Empire., Holy Roman. Bulla Aurea. Friedrich Creusner, 1474. https://collections.library.yale.edu/catalog/16189386.

APA, 6th edition

Empire., H. R. (1474). Bulla aurea. [Incunabula, Manuscript waste (Binding)]. Friedrich Creusner, https://collections.library.yale.edu/catalog/16189386.