Design for a Stained Glass Window with Two Unicorns, by Hans Holbein the Younger

Design for a Stained Glass Window with Two Unicorns. Pen and ink and brush, grey and watercolour washes, inner line in red chalk, 41.9 × 31.5 cm, Kunstmuseum Basel.
Holbein's makes his arch a part of the image rather than just a framing device. At the top, the structure and roof create the illusion of a deep-set building, which is contradicted by the narrowness of the lower supports. In the words of art historian Christian Müller "The portrayal is so convincing that the viewer is almost unable to to consider the impossibility of the subject" (Müller, 284).