During the first months of 1934 Escher worked on a series of prints of Rome by night. In a letter to Hein ‘s-Gravezande, dated 17 March 1940, he looks back on his nightly adventures;*
‘In the evening from 8 a.m. to 11 or 12 at night, I sketched in Rome, in this amazing, beautiful, night-time Rome, whose architecture I love so much more than I do during the day. All the excessive Baroque elements with which Rome is inundated (Rome is after all a Baroque city par excellence, despite the Roman and Medieval remains) fade at night. In addition, the modern indirect lighting with large spotlights, which have replaced the old-fashioned street lamps in the main areas, helps to increase the fantastic effect. If we ever go to Rome together (even a blind pig finds an acorn sometimes) I’ll show you around that Rome I love; then we will walk in the fantastic scenery, purified from people, as in a beautiful dream and then we will end up in one of the innumerable small popular pubs and drink a glass of Frascati to relax or, if you wish, to continue dreaming in that unreal world, as I only did after my life sceances.
I was drawing some picture on my folding chair. An electric flashlight hung from a button of my coat, indispensable especially since I was drawing on black paper with white chalk. Those are my fondest memories of Rome, those night tours. What curious encounters I had, and what a nice, awkward, obnoxious, and often moving audience surrounded my folding chair! I remember an old gentleman standing next to me for a long time without saying a word. Finally he asked politely if he was not bothering me by saying something. Not at all, I said. He found it wonderful, he said. I stopped and smiled fondly. A wonderful invention, he continued. Invention? I marveled; I just draw what I see! Yes, but that electric flashlight on the button of my coat, that indeed was a wonderful invention! …. I have also aroused some admiring expressions by “my leftness”. The fact that a left hand could draw interested them more than whether the result was any good. So I drew this way every evening and worked out the sketch the next day on wood’.
In each print Escher experimented with a different shading technique. The Mussolinian spotlights that illuminated the buildings provided sharp contrasts which he used to full effect in his woodcuts.
Source
[*] Wim Hazeu, M.C. Escher, Een biografie, Meulenhoff, 1998, page 163-164