A section of the remaining walls of the castra praetoria, the camp in Rome for the Praetorian Guard from 23 CE.
This image was first published on Flickr.
Original image by Ross Cowan. Uploaded by Mark Cartwright, published on 01 December 2016 under the following license: Creative Commons: Attribution-NonCommercial-ShareAlike. This license lets others remix, tweak, and build upon this content non-commercially, as long as they credit the author and license their new creations under the identical terms.