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, Incunabula in Yale Library]. Friedrich Creusner. https://collections.library.yale.edu/catalog/16189386.