Orenstein, 96-97; see this British Museum page for another drawing of Roman ruins, perhaps the Colosseum, recently attributed to Bruegel
doi.org
Morra, Joanne (2007). »Utopia Lost: Allegory, Ruins and Pieter Bruegel's Towers of Babel«. Art History. 30 (2): 200. doi:10.1111/j.1467-8365.2007.00538.x.