Here's a good page with early views of Petra in drawings done by David Roberts and two others
before Petra was restored, compared with pictures of Petra as it is today.
Drawing of the (former) arch by David Roberts/ (2 versions of this on a website)
One of two large earthquakes caused it tp break up. The latest was in 1927.
The narrowest section of the Petra Siq is about 3 feet across!