Detail of the antique city in the background of the Louvre St. Sebastian by Mantegna.
“The classical ruins are typical of Mantegna’s pictures. The cliffy path, the gravel and the caves are references to the difficulties of reaching the Celestial Jerusalem, the fortified city depicted on the top of the mountain, at the upper right corner of the picture, and described in Chapter 21 of John’s Book of Revelation.”
(via)