More free lessons at: http://www.khanacademy.org/video?v=5wptm7lPZyE
Francesco di Giorgio Martini (attributed), Architectural Veduta, c. 1490, oil on poplar, 131 x 233 cm (Gemäldegalerie, Staatliche Museen zu Berlin)

View this work up close on the Google Art Project: http://www.googleartproject.com/collection/gemaldegalerie/artwork/archit...