Recto: The Houses of the Barbarians (Vitruvius, Book 2, Chapter 1, nos. 3, 4); Verso: The Aeropagus in Athens with Cave Houses (Vitruvius, Book 2, Chapter 1, no. 5)., 1530?45, Pen and dark brown ink, sheet: 7 1/2 x 5 9/16 in. (19.1 x 14.1 cm), Drawin