
None of the images below are drawings but the results of rendering true 3D models.
Images marked * were published in the 2010 calendar "Illusies & Optische Fenomenen", published by Paul Baars.
The Romans were marvellous architects and engineers, as is evidenced by their aquaduct running from modern-day Uzès to Nîmes, which has a drop in height of 17m over its 50km length. However, I think even they would have had a bit of trouble constructing these.